Make dumps programmatically accessible.

[schwerdf]

Currently, Copper produces parser dumps by passing the entire internal representation of the grammar, LR DFA, and parse table into a "dumper" class for processing. This makes it difficult to extract any intermediate grammar information programmatically, such as is required for resolving issue #22.

This could be resolved by making use of the new schema for XML dumps (see issue #25), or by making the "dumpers" into event handlers, similar to how logging is currently handled. The latter would have the advantage of not circumscribing what is allowed to appear in a dump, so we could support different kinds of dumps for alternate pipelines.