File position matching changes

[mahrud]

This is an alternative to #36:

• Match file positions of the form -Foo[...]- for any "Foo"

cc: @d-torrance

[d-torrance]

Is the only difference between this and #36 that we're capturing the [[:alpha:]]+ so we don't need to decrement the match-beginning and match-end arguments?

I have no strong opinion either way -- just wanted to make sure I wasn't missing anything. :)

[mahrud]

Mostly yes, but also keeping the option of switching to something like \\(FilePosition|FunctionBody|...\\) later.