LR(k) parser construction.

TODO:
* conflict handling
  o statically
    o by priority
    o by associativity
  o dynamically
    o user-defined predicate
    o make attributes available
  o automatically
    o transparently change the grammar
  o can I use the same declarations for scanner and ll and lr?
  o scanner conflicts are usually solved implicitly, using
    sequencing information; this may become explicit
  o other tools
    o Eli
      o offers to change the lookahead
    o lex, yacc, syntax
      o priority for token; inherited to productions
      o priority for productions
      o associativity