Greplica

- Changed pypi tag from beta to stable

- Explicitly check for __main__ in __main__.py

- Shameless promotion on README (update pypi readme)

- Fixed bug with `FileDat.__eq__`

- Added type hinting
- Use an older version of Python 3.6 to test workflow to test backwards compatibility
- Explicitly sort files and directories in walk when recursing (test was occasionally failing without this)
- Added `start_index`, `stop_index`, and `num_matches` to `FileDat` with property alias `index` returning `start_index`

- GrepResult object is now returned from Grep.execute() (this is why the minor version number was bumped up)
- The GrepResult object contains FileDat, LineDat, InfoDat, and ErrorDat objects
- FileDat contains filename and index into lines where matching starts
- LineDat contains filename, line_num, byte_offset, and line
- InfoDat contains filename and info
- ErrorDat contains filename and err_str