Master branch nightly build depending on torch_nightly

We need a build of ignite to allow people try nightly version of PyTorch together with ignite. Since the PyTorch is nightly built, it might be better to call this package pytorch-ignite-nightly which is also a nightly build of master branch, but with the dependencies on torch changed to torch_nightly.

cc: @vfdev-5

NB: I’m not sure the dependency should be torch_nightly or torch-nightly, because the install command has torch_nightly but the output of pip says torch-nightly:

gaoxiang@pc ~ $ sudo pip install torch_nightly -f https://download.pytorch.org/whl/nightly/cpu/torch_nightly.html
Looking in links: https://download.pytorch.org/whl/nightly/cpu/torch_nightly.html
Collecting torch_nightly
  Downloading https://download.pytorch.org/whl/nightly/cpu/torch_nightly-1.0.0.dev20181029-cp37-cp37m-linux_x86_64.whl (85.9MB)
    100% |████████████████████████████████| 85.9MB 698kB/s 
Installing collected packages: torch-nightly
Successfully installed torch-nightly-1.0.0.dev20181029

@soumith Do you think we should change these two names to make them consistent?

[vfdev-5]

A link to keep it here: https://github.com/pytorch/pytorch/blob/master/tools/aten_mirror.sh May help to keep nightly branch update to master…

[vfdev-5]

@zasdfgbnm we have a CRON travis event that is used for building and uploading configured on nightly branch. Otherwise every master merge will produce a build/upload. Secondly, I do not want to expose nightly folder in master.