Rotations, grids, counting and speed boost

New operators: o for changing orientation, : for grids, - for logical difference, "" for quoted literals, e for edge segments. The inclusion operator # has been promoted to handle general counting of matches.

The matcher is much faster, since it now takes into account the possible sizes of expressions and won't try obviously wrong combinations.

Improved matching and context brackets

Implemented context brackets, which are abysmally slow. They should become faster later. New syntax also includes the label _ for the top-level expression.

The matching engine can now resolve any grammar where the matches can theoretically be resolved. Also fixed some bugs and added a tutorial.

Parser rewrite

The parser has been given a rewrite, and it supports comment lines. There's some new syntax, and especially the 0-area rectangles are now more logical. Examples have been put in their own folder.

Initial release

Implements all features listed in the PPCG post, but with different option syntax (backtick instead of comma).