stbt.Display: Cleanup: Use Gst.SECOND instead of 1e9
Merge pull request #220 from drothlis/draw-match-result

Refactor: Draw match rectangle using similar mechanism as draw_text
Refactor: Don't do any pyramid level changing inside `_match_template`
Refactor
_find_match is a generator
WIP: API: Add find_all

TODO:

* Documentation
* Tests for annotation
* Reduce duplication
fixup! WIP: API: Add find_all

(Fixes merge error)
Rename `find_all` to `match_all` (and `find_iter` to `match_iter`)

For consistency with `match`.
move `match_all` tests from stbt/__init__.py to tests/test-match.py
stbt.match_all returns an iterator; remove stbt.match_iter

Python seems to be going in the direction of everything being lazy if
possible (Python 3's `range` behaves like Python 2's `xrange`, etc).
You can use `list(match_all)` if you need to force the evaluation.
stbt.match_all docstring
fixup! stbt.match_all returns an iterator; remove stbt.match_iter
fixup! WIP: API: Add find_all

(Fix merge error after rebasing onto draw-match-result)
fixup! stbt.match_all returns an iterator; remove stbt.match_iter
No need to do `_draw_match` in finally block

...now that we have https://github.com/drothlis/stb-tester/pull/220
fixup! No need to do `_draw_match` in finally block

(Syntax -- no `finally` block anymore so the `try` isn't valid.)
fixup! No need to do `_draw_match` in finally block

(Thanks Will.)
Refactor common code from `match` and `match_all`

The private functions that implement our matching algorithm (`_matches`
and its helper `_find_matches`) now always yield at least one result. If
there were any matches (1 or more), they'll yield the matches. If there
were no matches at all, they'll yield a single result for the best (but
not good enough) match.

That way, `match` merely has to take the first result, and `match_all`
lazily filters out non-matches from the sequence.

This means we don't have to pass the `match_one` parameter around the
helper functions. I think this makes the code simpler.
Refactor: Rename `_matches` to `_find_matches`

And rename the previous `_find_matches` to `_find_candidate_matches`
(it's the first pass of the two-pass find-then-confirm algorithm).
Hopefully this naming makes the code slightly clearer.