GitLab

* testing with sox only when sox is available.

* use wav instead of mp3 for testing functions.

* typo.

* guard against not sox.

* backends definition.

* grouping backend functions into a separate file.

* remove duplicated code.

* requires sox.

* replace by wav, requires sox.

* require with scope.

* undo alignment.

* requires sox for these two, because of mp3.

* no longer need first mp3.

* cleaning.

* new wav version of file.

* flake8.

* remove unnecessary load.

* flake8.

* lint.

* lint.

* revert formatting of file.

* merging into common_utils.

* docstring.

* rename to common_utils.

- Apply __future__ imports uniformly (future division is the biggy, but absolute
  imports mattered too)
- Hotfix use of tempfile.TemporaryDirectory using a BC library (DO NOT
  add this library as a dependency to torchaudio; it's only for testing)
- Replace math.gcd with fractions.gcd
- Fix a weird pytest collection bug involving parametrized tests
- Turn on Python 2 and Python 3.7 in Travis.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>