Add universal weather data downloader

[dchassin]

This PR adds support for NREL NSRDB weather data.

Current issues

None

Code changes

• Add python_extras/nsrdb_weather.py subcommand utility.
• Fix module/tape/tape.cpp bug in parsing of raw timestamps.
• Add support for ${GEOCODE <lat>,<log>[#<res>]} and ${GEOCODE <obj>[#<res>]}
• Add support for #ifmissing <filename> macro.

Documentation changes

• See gridlabd nsrdb_weather help.
• Add GLM/Macro/Ifmissing documentation
• Add GLM/Global/Geocode documentation

Test and Validation Notes

You need to sign up for the data service using the gridlabd nsrdb_weather --signup=<your-email> command.

To run a self-test, use the command gridlabd nsrdb_weather --test. This should create two files, test.glm and test.csv. If it fails, an error/exception will be displayed and the exit code will be non-zero.