Issue #55 PPI::Token::Prototype->prototype does not strip parens/whitespace as documented

Fixes issue #55 - PPI::Token::Prototype->prototype does not strip parens/whitespace as documented.  Adds unit tests for PPI::Token::Prototype.

Fixes issue #50 - PPI::Token::Prototype::__TOKENIZER__on_char uses capture var in undefined state (this issue was a false alarm, but the code was changed to make it clearer.)