urlutil: add a `get_push_paths` to perform the push destination logic As is this changeset does not change anything. However having an official empty point will help unifying the logic and encapsulate the details and update the logic to support path definition pointing to multiple other path. Differential Revision: https://phab.mercurial-scm.org/D10377

urlutil: extract `parseurl` from `hg` into the new module The new module is well fitting for this new code. And this will be useful to make the gathered code collaborate more later. Differential Revision: https://phab.mercurial-scm.org/D10375

urlutil: extract `url` related code from `util` into the new module The new module is well fitting for this new code. And this will be useful to make the gathered code collaborate more later. Differential Revision: https://phab.mercurial-scm.org/D10374

urlutil: extract `path` related code into a new module They are a lot of code related to url and path handling scattering into various large module. To consolidate the code before doing more change (for defining "multi-path"), we gather it together. Differential Revision: https://phab.mercurial-scm.org/D10373

help: document the `path://` url scheme If we want people to use it, we need to document it. Differential Revision: https://phab.mercurial-scm.org/D10372

help: point to `hg help urls` in `hg help config.paths` This seems useful to point at what people can put as value for these config. Differential Revision: https://phab.mercurial-scm.org/D10371