This change completes my testing of decorator parsing for now. It tests the token
`*[]map[string]map[()*(bool,string,test/package:test/module/Crazy)number][][]test/package:test/module/Crazy`.
This turned up some bugs, most notably in the way we returned the "full" token for
the parsed types. We need to extract the subset of the token consumed by the parsing
routine, rather than the entire thing. To do this, we introduce a tokenBuffer type
that allows for convenient parsing of tokens (eating, advancing, extraction, etc).
5260ff9313