Renamed import nickname so that the source of two routines would not be confused.

Added a GNSS TEC instrument.

Applied code review feedback and new style standards, which include:
- spelling,
- fixing filename to use 2-digit year, split between 1900s and 2000s,
- init and clean docstrings,
- correct join string for acknowledgements, and
- attaching acknowledgements and references.

Updated to:
- remove python 2.7 support,
- improve docstrings,
- remove unnecessary comments, and
- apply new standards for acknowledgements and references.

Fixed logging call and extraction of list of keys.

Adapted the general load routine for loading data from an HDF file to allow
different data variables to depend on different coordinates.  This will make the loaded data set smaller, since less padding will be needed and non-unique
values will not need to be maintained.

Removed the initial support for 'los' data and updated 'vtec' load to use new
xarray loading capabilities.

To have a tuple with a length attribute, a comma needs to be included after the variable.

Updated example in docstring and fixed bug where variable name retrieval
from xarray wasn't correctly obtaining a list of keys.

Fixed bug introduced by assuming merge was done in place.

Remove the madrigal keywords as cooridinates for data variables, but keep
them as float coordinates.

Created docs directory and added VTEC figure for future examples.

Fixed incorrectly specified units in the VTEC meta data.

Ran flake8 locally on files and made PEP8 corrections.

Fix word repetition in the methods/madrigal docstrings.

Co-authored-by: Russell Stoneback <rstoneba@utdallas.edu>

Use the metadata units_label to fix the TEC units.

Co-authored-by: Russell Stoneback <rstoneba@utdallas.edu>

Fixed grammar in docstring.

Co-authored-by: Russell Stoneback <rstoneba@utdallas.edu>

Generalized second instance of units label in metadata.

Co-authored-by: Russell Stoneback <rstoneba@utdallas.edu>

Fixed bug where dropped duplicates didn't consider coordinates, and so removed unique data values.

…o tec_inst

Updated reference figure to hold all of the data.

Found a bug in running with one additional coordinate when loading JRO ISR drifts data.  Fixed by setting data column length variable before 'time' is added and ensuring everything higher dimensional is an xarray.

Reverted the determination of the data column length location and fixed ValueError text to be more helpful.

Updated loading method for all JRO ISR data types to use new features of the
loading routine.  This fixes a bug in the implementation and also reduces the
amount of duplicate data stored.

Updated install_requires to include netCDF support and added tag for only supporting Python 3.

Added general support for downloading and loading netCDF data from Madrigal and applied this as the default in the GNSS TEC instrument module.

Updated the PiPy distribution name for netCDF4-Python.

Develop update for PR #11

Have Travis use develop-3, since enough breaking changes have been made.

Module nickname was not carried through entire file, fixed this.

Removed hopefully the last instance of sat_id.

Replaced print statements with logger warnings.

Added a file_format flag option to JRO ISR load and download routine.

Added ability to remove expected coordinates from
HDF5 xarray loading if they aren't present.  Now
only errors if all variables are absent.

Flake8 correction for hanging indent.

Updated general madrigal routines by:
- fixing incorrect use of `self` in `filter_data_single_date`,
- changing `Notes` to `Note`,
- ensuring local files have the right extension,
- changing variable `file_format` to `file_type`
  to remove any confusion with the Instrument
  attribute,
- changing `netcdf4` to `netCDF4` everywhere, and
- specifying accepted file types.

Allow pysat to handlee multiple TEC file formats, though instruments will only load one type at a time.

Fixed bug assigning time index, now is an index of datetime values.

Fixed bug that tried to set file_type multiple times.

Adapted code to allow flexible file types, removed
unused default function call, and updated the style
and docstrings in clean.

Updated jro_isr to use flexible file type throughout
instrument, and changed old variable name.

More efficient transfer from unix to timestamp.  Fixed bug where index does not need to be assigned.

Several suggestions from code review, including code style and docstring typos.

Co-authored-by: Russell Stoneback <rstoneba@utdallas.edu>