Support quickfix

[kana]

Currently it's not possible to use quickfix from vspec's output, because there is no assistive information to jump to failed examples.

[kana]

There are two candidates as locations of failed examples:

• Failed :Expect — but it might be called from a function rather than :it. In that case I want to grasp the entire stack trace to investigate causes of a failure. Unfortunately it's not possible to get locations of all but last functions in a stack trace. Perhaps it might be better to change the style of such tests.
• :it that contains a failed :Expect