Implement GitHub

Adds support for GitHub in the form `foo/bar` or `foo/bar#tag` via the
GitHub archives
require path, rename response to res
add failing test for retry
Retry tarballs
Merge branch 'fix/retry-tarball' of github.com:ForbesLindesay/npm-fetch into tarball.js

Conflicts:
	lib/tarball.js
make if statement more readable
more tests
Merge branch 'tarball.js' into implement/github
Tests for github

One is telephoning to github so we might want to mock
this one with nock or something like this in future
set rimraf to 2.1.4
Merge pull request #14 from ForbesLindesay/tarball.js

Tarball.js
Merge pull request #4 from ForbesLindesay/implement/github

Implement GitHub
Implement npm.version
Simplify registry config for npm.version
Introduce testserver.js

Introduce a simple, easy configurable testserver
Closes #17
Merge pull request #19 from ForbesLindesay/fix/testserver-dry

Introduce testserver.js
cleanup: remove unused file and semicolons
Merge pull request #18 from ForbesLindesay/fix/stuff

cleanup: remove unused file and semicolons
Release 0.0.1
Add tests for the npm.tag

Fixes #22