Initial alpha release

Added

• Method df.tonumpy() now has argument stype which will force conversion into
  a numpy array of the specific stype.
• Enums stype and ltype that encapsulate the type-system of the datatable
  module.
• It is now possible to fread from a bytes object.
• Allow columns to be renamed by setting the names property on the datatable.
• Internal "MemoryMapManager" will make datatable more robust when opening a
  frame with many columns on Linux systems. In particular, error 12 "not enough
  memory" should become much more rare now.
• Number of threads used by fread can now be controlled via parameter nthreads.
• It is now possible to supply string argument to dt.DataTable constructor,
  which in turn will try to interpret that argument via fread.
• fread can now read compressed .xz files.
• fread now automatically skips Ctrl+Z / NUL characters at the end of the file.
• It is now possible to create a datatable from string numpy array.
• Added parameters skip_blank_lines, strip_white, quotechar and dec to fread.
• Single-column files with blank lines can now be read successfully.
• Fread now recognizes \r\r\n as a valid line ending.
• Added parameters url and cmd to fread, as well as ability to detect URLs
  automatically. The url parameter downloads file from HTTP/HTTPS/FTP server
  into a temporary location and reads it from there. The cmd parameter executes
  the provided shell command and then reads the data from the stdout.
• It is now possible to pass file objects to fread (or any objects exposing
  method read()).
• File path given to fread can now transparently select files within .zip archives.
  This doesn't work with archives-within-archives.
• GenericReader now supports auto-detecting and reading UTF-16 files.
• GenericReader now attempts to detect whether the input file is an HTML, and if so
  raises an exception with the appropriate error message.
• Datatable can now use either llvm-4.0 or llvm-5.0 depending on what the user has.
• fread now allows sep="", causing the file to be read line-by-line.
• range arguments can now be passed to a DataTable constructor.
• datatable will now fall back to eager execution if it cannot detect LLVM runtime.
• simple Excel file reader.
• It is now possible to select columns from DataTable by type: df[int] selects
  all integer columns from df.
• Allow creating DataTable from list, while forcing a specific stype(s).
• Added ability to delete rows from a DataTable: del df[rows, :]
• DataTable can now accept pandas/numpy frames with columns of float16 dtype
  (which will be automatically converted to float32).
• .isna() function now works on strings too.
• .save() is now a method of Frame class.
• Warnings now have custom display hook.
• Added global option nthreads which control the number of Omp threads used
  by datatable for parallel execution. Example: dt.options.nthreads = 1.
• Add method .scalar() to quickly convert a 1x1 Frame into a python scalar.
• New methods .min1(), .max1(), .mean1(), .sum1(), .sd1(), .countna1()
  that are similar to .min(), .max(), etc. but return a scalar instead of a
  Frame (however they only work with a 1-column Frames).
• Implemented method .nunique() to compute the number of unique values in each
  column.
• Added stats functions .mode() and .nmodal().

Changed

• When writing "round" doubles/floats to CSV, they'll now always have trailing zero.
  For example, [0.0, 1.0, 1e23] now produce "0.0,1.0,1.0e+23" instead of "0,1,1e+23".
• df.stypes now returns a tuple of stype elements (previously it was returning
  a list of strings). Likewise, df.types was renamed into df.ltypes and now it
  returns a tuple of ltype elements instead of strings.
• Parameter colnames= in DataTable constructor was renamed to names=. The old
  parameter may still be used, but it will result in a warning.
• DataTable can no longer have duplicate column names. If such names are given,
  they will be mangled to make them unique, and a warning will be issued.
• Special characters (in the ASCII range \x00 - \x1F) are no longer permitted in
  the column names. If encountered, they will be replaced with a dot ..
• Fread now ignores trailing whitespace on each line, even if ' ' separator is used.
• Fread on an empty file now produces an empty DataTable, instead of an exception.
• Fread's parameter skip_lines was replaced with skip_to_line, so that it's
  more in sync with the similar argument skip_to_string.
• When saving datatable containing "obj64" columns, they will no longer be saved,
  and user warning will be shown (previously saving this column would eventually
  lead to a segfault).
• (python) DataTable class was renamed into Frame.
• "eager" evaluation engine is now the default.
• Parameter inplace of method rbind() was removed: instead you can now rbind
  frames to an empty frame: dt.Frame().rbind(df1, df2).

Fixed

• datatable will no longer cause the C locale settings to change upon importing.
• reading a csv file with invalid UTF-8 characters in column names will no longer
  throw an exception.
• creating a DataTable from pandas.Series with explicit colnames will no longer
  ignore those column names.
• fread(fill=True) will correctly fill missing fields with NAs.
• fread(columns=set(...)) will correctly handle the case when the input contains
  multiple columns with the same names.
• fread will no longer crash if the input dataset contains invalid utf8/win1252
  data in the column headers (#594, #628).
• fixed bug in exception handling, which occasionally caused empty exception
  messages.
• fixed bug in fread where string fields starting with "NaN" caused an assertion error.
• Fixed bug when saving a DataTable with unicode column names into .nff format
  on systems where default encoding is not unicode-aware.
• More robust newline handling in fread (#634, #641, #647).
• Quoted fields are now correctly unquoted in fread.
• Fixed a bug in fread which occurred if the number of rows in the CSV file was
  estimated too low (#664).
• Fixed fread bug where an invalid DataTable was constructed if parameter max_nrows
  was used and there were any string columns (#671).
• Fixed a rare bug in fread which produced error message "Jump X did not finish
  reading where jump X+1 started" (#682).
• Prevented memory leak when using "PyObject" columns in conjunction with numpy.
• View frames can now be properly saved.
• Fixed crash when sorting view frame by a string column.
• Deleting 0 columns is no longer an error.
• Rows filter now works properly when applied to a view table and using "eager"
  evaluation engine.
• Computed columns expression can now be combined with rows expression, or
  applied to a view Frame.