Implement OPL reader and exporter for CSV and JSON files

Closes #18 (closed)

Added

• New generic OPL CSV and JSON reader and exporter
• Add OPL CSV to JSON and JSON to CSV convertor
• New OPL JSON schema
• Add a new depreciated method in misc sub-module.

Changed

• Strip trailing .000Z to Z in datetime formatter.
• Change majis.itl.csv.export.save_csv to majis.itl.csv.export.save_itl_csv.
• Change majis.itl.csv.export.save_xlsm to majis.itl.csv.export.save_itl_xlsm.
• Move JSON schemas into their own submodule.
• MAJIS_ITL_SCHEMAS is replaced by MAJIS_SCHEMAS as a dict to support OPL schemas.

Fixed

• Read the docs jupyter-book configuration (closes #16 (closed)).

Depreciated

• Legacy save_csv and save_xlsm are depreciated in favor of save_itl.