Don't allow special characters in package names

[Frozenfire92]

Using the generator I thought I would be cheeky and use a semicolon at the end of my package name. This is a very bad idea and would be good to check for this before the package is even created.

[MicahZoltu]

I believe a better more scalable solution would be for atom to fully support UTF-8 package names, including any "special" characters like semicolons. Assuming package-generator is written by different people though, they may not have control over Atom's handling of package names.