Annotations for rules

This realizes feature for annotations of rules. This annotations may be used by compiler passes for some purposes, for example, per-rule memoization or for creating template rules. Example:
```
// This example only for demonstraiting parsing. Template rules not yet reaized

// After realize template parameters for rules invocations, template rules may be
// realized with @Template annotation.
start = List<'*', ','>;

@Memoize
@Template(item, delimiter)
List
  = h:(i:item delimiter {return i})* t:item? {
    if (t) h.push(t); return h;
  };
```
This pull request can be considered, as the first part of implementation #45.

Annotations looks similarly to annotations in Java: it can have optional parameters (which an identifiers). Any rule can have any count of annotations, it stored in `annotations` field in rule AST node.