Release 0.3.1

Added

• Added ability to delete rows from a view Frame.
• Implement countna() function for obj64 columns.
• New option dt.options.core_logger to help debug datatable.
• New Frame method .materialize() to convert a view Frame into a "real" one.
  This method is noop if applied to a non-view Frame.
• Several internal options to fine-tune the performance of sorting algorithm.
• Significantly improved performance of sorting doubles.
• fread can now read string columns that are larger than 2GB in size.
• fread can now accept a list/tuple of stypes for its columns parameter.
• improved logic for auto-assigning column names when they are missing.
• fread now supports reading files that contain NUL characters.
• Added global settings options.frame.names_auto_index and
  options.frame.names_auto_prefix to control automatic column name
  generation in a Frame.

Changed

• When creating a column of "object" type, we will now coerce float "nan"
  values into Nones.
• Renamed fread's parameter strip_white into strip_whitespace.
• Eliminated all assert() statements from C code, and replaced them with
  exception throws.
• Default column names, if none given by the user, are "C0", "C1", "C2", ...
  for both fread and Frame constructor.
• function-valued columns parameter in fread has been changed: if previously
  the function was invoked for every column, now it receives the list of all
  columns at once, and is expected to return a modified list (or dict / set /
  etc). Each column description in the list that the function receives carries
  the columns name and stype, in the future format field will also be added.

Fixed

• fread will no longer consume excessive amounts of memory when reading a file
  with too many columns and few rows.
• fixed a possible crash when reading CSV file containing long string fields.
• fread: NA fields with whitespace were not recognized correctly.
• fread will no longer emit error messages or type-bump variables due to
  incorrectly recognized chunk boundaries.
• Fixed a crash when rbinding string column with non-string: now an exception
  will be thrown instead.
• Calling any stats function on a column of obj64 type will no longer result in
  a crash.
• Columns/rows slices no longer fail on an empty Frame.
• Fixed crash when materializing a view frame containing obj64 columns.
• Fixed erroneous grouping calculations.
• Fixed sorting of 1-row view frames.