Extracted useful elements of the `load` function to allow their use elsewhere without code duplication.

Added type-specific GNSS load functions and exploratory file functions for the line-of-sight files.

Added support for the line-of-sight (los) TEC data.

Improved the GNSS instrument method description to encompass the new scope.

Added a summary of the changes to the changelog.

Removed excess lines, fixed typos, added missing imports.

Added missing return value to the docstring.

Added two load options for the GNSS TEC LoS tests.

Allow creation of an empty Dataset from an empty DataFrame.

Allow an empty filelist to be provided and create an empty data object.

Allow the GNSS TEC load to work with an empty file list.

Added load tests for the LoS logger warning and ValueError.

Removed unused variable and fixed indentation.

Corrected the download test flag.

Co-authored-by: Jeff Klenzing <19592220+jklenzing@users.noreply.github.com>

Fixed the clean method to have an informative message for the LoS data.  Also removed inaccessable line in the load method.

Added a test for the gnss_tec load method ValueError raised if a bad `los_value` is supplied.

Added unit tests for uncovered lines in the general instruments methods sub-module.  Also improved style for Error tests.

Added a test for loading no data in the `load_los` function, additionally testing the time selection set-up.

Added a coveralls service job environment variable.

Needed to get the right dict from the setup.

Add a fake file to test the load failures.

Fixed import order to be alphabetical.

Updated coveralls to run in parallel.

Disabled local LoS download tests, also added a warning for users attempting downloads.

Removed old test line.

Updated the version caps for coveralls, sphinx, and sphinx_rtd_theme.

This reverts commit 9b8919b.

Removed a test variable that was being used for an incorrect purpose.

Removed extra 'run' from workflow.

Updated the coveralls line in the RC CI test.

Added the 'url' kwarg to the DMSP IVM download method, since UTD downloads were failing at the central site.

Removed the URL kwarg, local tests didn't need the url change.

Added a missing index for the test list.