Speedy-antlr-tool

* Change entry rule name lookup to use map instead of massive if/else (7)
* Add ability to prune down list of allowed entry rule contexts.

**Changes**
* Update C++ templates to support static casting introduced by latest Antlr runtime (4.9.3)

**Changes**
* Add support for grammars that are split into separate lexer/parser files (5)

Initial release!