Pkg.generate features

I am working to close #4908, #8267, #8144. This should also supplant #7809.

I have added the following licenses for #4908, #7809:
* GPLv2 
* LGPLv2
* CC0

This also publicizes the licenses better when `Pkg.generate()`, `Pkg.generate("MyPkg")`, or `Pkg.generate("MyPkg", "WithAnInvalidLicense")` is called.
 
Generation now initializes with a .gitignore for `*.jl.cov`, `*.jl.mem`.

Possibly contentious:
I've added code coverage by default into the .travis.yml file and the corresponding badge to the readme. Code coverage has helped improve my code quality and helps significantly with debugging. I am not sure how people feel about promoting coveralls.io by default, but it seems to be the best free option.
Can Coveralls show the code coverage for just the master branch as well?