Pyirtam

* Updated README to include instructions and fix DOI, Coverage badges
* Fixed documentation links and updated the installation guide

* Added a function to retrieve the IRTAM coefficients
* Added a module for IRTAM coefficient functions
* Added unit tests for the IRTAM coefficient functions
* Updated library functions to specify use of subdirectories and removed unused
args
* Added a package-level directory to store IRTAM coefficients, if desired
* Removed a broken link from the documentation

* Fixed import bug, changing the name of the primary sub-module
* Added an error catch for bad IRTAM directory input and unit tests for this
* Added badges to the README

* Added community documents
* Added .zenodo.json file
* Added readthedocs build support and badges
* Fixed PEP8 style by removing extra white space, unused imports, and reducing
duplicate code

* Alpha release