lexer declarations and constructor extension

[sirkon]

Having @lexer::members support for Go target is not enough. Just like C++, Go needs @lexer::declarations to add needed fields into a lexer and I also added @lexer::construction block (I don't know how you call it in ANTLR4) to extend New<Gramman Name>Lexer constructor code.

This is how I used this:

...

@lexer::declarations {
    comments map[int]map[int]string // This adds a new field "comments"
}

@lexer::construction {
    l.comments = map[int]map[int]string{} // This inits "comments" field in the constructor
}

...

[KvanTTT]

This line looks like leftover of conflict resolving. Please remove.

[sirkon]

Oops, removed. Removed the last line too.

[KvanTTT]

Now there is no need to change this file. Please revert.