Fix publishing

This moves generation  to prepublishing, as well as asynchronizes dependency loading for libssh2/libgit2/http_parser.

It also only installs devdeps if required now, (and I would like to make it uninstall them when its finished, if i can detect a few things).

Unfortunately, short of publishing some beta tag to npm, or publishing to a fake NPM repo, i have no idea how to test the actual publishing.