SLL decisions

[sharwell]

• Allow restriction of individual decisions to SLL prediction
• Blocks in parsers support an sll=true; option to explicitly specify

Here is an example:

ifStmt
  : 'if' '(' expr ')' stmt
    ( options{sll=true;}: 'else' stmt
    | /*empty*/
    )
  ;

[sharwell]

This update provides a much cleaner solution to #42.

[parrt]

This would make expressions non-LL per force but you'd have to be sure they are not stack sensitive.