Vendor in packages

[stuaxo]

• [ ] asyncronousfilereader - removing our internal copy.

Later on we can do:

• [ ] scandir (only for python2) + move directory iteration to scandir
• [ ] virtualenv functions can be spun out to their own library

These libraries can live in _vendor and use git submodules.

[stuaxo]

Closing - asyncronousfilereader is vendorized, other things will happen as needed.