grammar: implement a (possibly conflicted) Grammar class.
Shift/reduce and reduce/reduce conflict resolution to come.

Signed-off-by: Peter Williams <pwil3058@gmail.com>
grammar: change from detecting conflicts to resolving them

Signed-off-by: Peter Williams <pwil3058@gmail.com>
grammar: modify resolution process and use them on Grammar initialization.

Signed-off-by: Peter Williams <pwil3058@gmail.com>