Fix gridlabd-library subcommand

[dchassin]

This PR fixes issue #979.

Current issues

• The organization name has to be defined in the path i.e. US/CA/SLAC is not used as default and has to be specified

Code changes

• Fixed curl usage and internal variable so they refer to correct github repo folders.
• Add -l|--library options

Documentation changes

• Add /Command/Library

Test and Validation Notes

None

[aivanova5]

Support for -l and --library can not find the files

**aivanovalocal@PC99458 docker % gridlabd library index 
overhead_line_conductors.glm
wood_pole.glm
aivanovalocal@PC99458 docker % gridlabd -l wood_pole.glm
ERROR    [INIT] : unable to load '/usr/local/opt/gridlabd/4.2.26-210817-develop_fix_library/share/gridlabd/library/wood_pole.glm': No such file or directory
FATAL    [INIT] : shutdown after command line rejected**