Parse "yield" on its own

Thinking this should be a separate type in the parser so we can capture
this separately from call expressions and references to variables.
Parse character literals

Surprised to find this was a feature of ruby! Seems antiquated in a post ruby 1.9
world, but perhaps there are good performance reasons for this?
Show 100 extra characters of context around parse errors

Seems to be occuring around '?' mostly. First it was method names when defining
a method, now it's globals. Fully expect to see this around ternary logic soon.