Add support for non-repository packages

[noteflakes]

Sometimes a repository is overkill. Sometimes people don't want to use git. Lyp should be able to install packages from plain urls, or even from stdin.

# local file (already supported)
$ lyp install mypack@ly-code/mypack.ly

# from stdin
$ cat ly-code/mypack.ly | lyp install mypack -

# plain http(s)
$ lyp install http://myserver.com/mypack.ly

# archive on https
$ lyp install http://myserver.com/mypack.tar.gz

# gists
$ lyp install gist.github.com/ciconia/22e96b33463a8ae4b7df
$ lyp install gist:ciconia/22e96b33463a8ae4b7df

[noteflakes]

What's needed to achieve installing packages from single files:

• canonical naming:
  • conversion of package refs (normally URLs) to local package path under ~/.lyp/packages.
  • way to explicitly name a package regardless of its URL, for example:

  $ lyp install events://noteflakes.com/some/random/path
  $ lyp install demopackage:https://noteflakes.com/foo.bar