Adding some doc comments

Hey,

I was adding some doc comments. Going through the code, I have fixed a few PSR inconsistency.

Some of the things I noticed are

1 ) PackageXmlParser and 2 ) PackageJsonParser have a different api. 

In one you are expecting a directory path, in the other you expect the .json path. I feel it is worth to change.

Also the gitIgnoreFiles method seems spread, seems some sort of refactoring is good.

Thanks
Let me explain:
- This command should be named 'release' as it  makes the tree release ready
- It actually create an Archive (extname-<version>.tgz, but that should be optional (final version of pickle should work when using only git)
- Eventually create an Archive class but sounds a bit too much as it is just one function

Does it make more sense?