GitLab

Billing of changes:

* Can now toggle what branch is built using BRANCH envvar
* PyTorch nightly we were built against is hardcoded into conda meta.yaml
* Disable Conda Python 3.5 builds as we don't have nightlies for torch at the moment
* No more torchaudio-cpu or torchaudio-nightly suffix
* Remove librosa from testing stanza, so that conda build works with stock anaconda channel
* Change convention on PREFIX to be what we previously called $PREFIX/audio
* Make build_from_source.sh cd-neutral

Signed-off-by: Edward Z. Yang ezyang@fb.com