[antlr-interest] big changes to action spec in v3

[Terence Parr]

Howdy,

Spent all day altering how you specify actions outside of  
productions.  I wanted something much more flexible and here is the  
comment from the README.

Ter
---------------
* action syntax changed "@scope::actionname {action}" where scope  
defaults
   to "parser" if parser grammar or combined grammar, "lexer" if  
lexer grammar,
   and "treeparser" if tree grammar.  The code generation targets decide
   what scopes are available.  Each "scope" yields a hashtable for  
use in
   the output templates.  The scopes full of actions are sent to all  
output
   file templates (currently headerFile and outputFile) as attribute  
actions.
   Then you can reference <actions.scope> to get the map of actions  
associated
   with scope and <actions.parser.header> to get the parser's header  
action
   for example.  This should be very flexible.  The target should  
only have
   to define which scopes are valid, but the action names should be  
variable
   so we don't have to recompile ANTLR to add actions to code gen  
templates.

   grammar T;
   options {language=Java;}
   @header { package foo; }
   @parser::stuff { int i; } // names within scope not checked;  
target dependent
   @members { int i; }
   @lexer::header {head}
   @lexer::members { int j; }
   @headerfile::blort {...} // error: this target doesn't have  
headerfile
   @treeparser::members {...} // error: this is not a tree parser
   a
   @init {int i;}
     : ID
     ;
   ID : 'a'..'z';

   For now, the Java target uses members and header as a valid name.   
Within a
   rule, the init action name is valid.