Initial sgf processing

[AtrusRiven]

Added basis support for sgf files:

• Parsing: The sgf_parse() function parses the sgf file for further processing.
• Preprocessing:
  • Metadata: The sgf_metadata_dict() function transforms the metadata part to a dictionary for further processing.
  • Moves: The sgf_moves() function returns the moves part.
• Finalizing:
  • Metadata: The sgf_metadata_table() function converts the metadata dictionary to a table.
  • Moves: The sgf_moves_board() function returns the moves for inclusion in stones attribute of go-board function.

[AtrusRiven]

Any chance for merging the PR? :-) Thanks!