WIP: Added new initializers

[joaogui1]

Adding kaiming uniform and normal and lecun uniform and normal initializers, besides adding the more general variance scaling initializer

[joaogui1]

I believe I'm done here

[lukaszkaiser]

In addition to the changes below, please make sure each initializer is at least ran once in initializers_test -- that'd catch the syntax errors that were left here (running pylint is also enoucraged).

[joaogui1]

Implemented the requested changes

[lukaszkaiser]

There were unnamed variables, so the tests should have failed. It's strange if the test passed with this code. Please correct the code and run the tests manually to make sure they pass.

[joaogui1]

Fixed those parts and testes on my machine, should work now

[lukaszkaiser]

Looks good, thanks!