CTPG 1.2.0

Two things:
1. An example of simple language parser that builds an abstract syntax tree.
https://github.com/peter-winter/ctpg/tree/master/examples/language

2. New functors dealing with common list tasks in typical scenarios when rules use recurrence to formulate lists of the same constructs.

See: https://github.com/peter-winter/ctpg#functor-helpers, precisely the push_back and emplace_back functors.