feat: add support for train on windows

[Wang-zipeng]

Implement train on windows. Compile steps(need visual studio 2017):

1. Setup compile environment: execute "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat" in the windows cmd to establish a compile environment.
2. execute "set DISTUTILS_USE_SDK=1"
3. Compile enter the code folder and use command "python setup.py develop"

Train steps:

1. enter the "playground\centernet.res18.coco.512size" folder and run "python train_net.py" or run in the IDE like pycharm. If you want to run in the pycharm be attention set python.exe's path in the PATH environment variable.
2. If you want to train resnet50/101, just copy train_net.py to the "playground\centernet.res50.coco.512size" or "playground\centernet.res101.coco.512size"

Anothers:

1. Because we can't use "os.statvfs" on the windows so i remove the disk check, and i think it doesn't matter.
2. Because we can't use "os.getuid()" on the windows so i set a constant name as "User_name", and i think is impossible to train on windows cluster.

[Wang-zipeng]

PTAL @Wang-zipeng

i just search PTAL's mean by google.