Grammar for method invocation

This is an interim pull-request, to avoid merge hell.

The parser now recognizes method invocation (`[int]::Parse()`), but that's all - no AST for it, let alone execution.

Irony's Grammar Explorer now reports 0 Reduce/Reduce errors. As these errors indicate serious problems in the grammar, this is good news.

It reports 4 Shift/Reduce errors, which is way down from previous numbers.

I added a unit test to lock down the number of grammar errors, so we can drive it to 0 and keep it there.