Add NETL methods, main.py, and YAML settings file

[gschivley]

This is a big PR with lots of changes. Some are smaller (docstrings on some of the existing EPA functions) but many are major.

New NETL methods:

• Add upstream data and processes for import to OpenLCA. This is only implemented for the NETL methods because I haven't had time to test if it would work with existing EPA methods.
• Add a new IO-based trading method for BA or FERC regions
• Add a modified method to calculate generation processes that uses groupby rather than nested for loops (talk to @jump2conclusionsmatt about this).
• Ability to included a "mixed" fuel category for plants that aren't 90% single-fuel.
• Create fuel mix processes using 923 data for a specific year.

Change the settings/config file file from JSON to YAML:

• YAML allows for descriptive comments, which will make it easier for users to understand what the parameters are used for.
• Changed model_config.py to select the YAML file instead of JSON files.
• Added pyyaml to the setup.py requirements list.

Add a main.py:

• This file can be run from the command line and will make use of all options selected in the YAML file.

Other changes (not comprehensive):

• Split the large function in generation.py in two, just to make it a little easier and allow users to output data part-way through as a dataframe if they want to.
• Add a new module for download of EIA923 data (eia923_generation.py).
• Add docstrings to many existing functions and most of the new functions.
• Change a few of the functions in __init__.py so that they can output results for either the existing EPA or new NETL methods.

[gschivley]

@WesIngwersen There are a few more changes from @jump2conclusionsmatt coming through on this PR but I wanted to get it in your queue. I didn't get as far with merging the two methods as I would have liked but I think we've made a significant push.

[m-jamieson]

In combinator.py, ln 17 and 20 'sheetname' must be replaced with 'sheet_name' because of pandas deprecation of sheetname

I'm getting an error in reading in EIA fuel receipts in read_eia_923_fuel_receipts File "C:\Users\wesle\AppData\Local\Programs\Python\Python37\lib\site-packages\xlrdinit.py", line 157, in open_workbook ragged_rows=ragged_rows, File "C:\Users\wesle\AppData\Local\Programs\Python\Python37\lib\site-packages\xlrd\book.py", line 92, in open_workbook_xls biff_version = bk.getbof(XL_WORKBOOK_GLOBALS) File "C:\Users\wesle\AppData\Local\Programs\Python\Python37\lib\site-packages\xlrd\book.py", line 1278, in getbof bof_error('Expected BOF record; found %r' % self.mem[savpos:savpos+8]) File "C:\Users\wesle\AppData\Local\Programs\Python\Python37\lib\site-packages\xlrd\book.py", line 1272, in bof_error raise XLRDError('Unsupported format, or corrupt file: ' + msg xlrd.biffh.XLRDError: Unsupported format, or corrupt file: Expected BOF record; found b'Plant Id'

Sorry about this - this has actually already been done in a pull request to Schivley's master that should automatically get pulled into this request on acceptance.

[gschivley]

I approved the PR by @jump2conclusionsmatt to this branch. Should be accessible here now.