closes #54

Changes:
 - `browse` and `compare` always open HTTPS
 - the `-p` flag for these commands has no effect anymore
 - updated `browse` URL for wiki pages
 - cherry-picking a URL doesn't add a new remote as private

references a01b256f

closes #63

New implementation allows for any number of chained commands.
The main command executes between "before" and "after" execution.

Commands can be simple strings, argument arrays or procs.

closes #64

A git remote can be configured with multiple "url" values.
Read them all in and pick the first GitHub one.

Closes #59

Hub::Context methods were public, now they are private. Ensures that
`Hub::Commands.respond_to?` doesn't return true for any of its methods.

Closes #62

hub would erroneously display the help page instead of forwarding the
arguments to git.

Bonus: make test/fakebin/git POSIX shell compatible; was using bashisms.

Closes GH-56.

Also, new version of webmock deprecates including the "WebMock" module

Some tests relied on the current working directory being named "hub".
This change makes it possible for tests to stub out the name of the
current directory.

References 9801b465

Apart from "-t" not being supported by zsh's `type`, it does not appear
to work with bash, too.

Fixes: http://github.com/defunkt/hub/issues/#issue/47

The completion for git 1.7.2 parses the output of `git help --all`
to generate a list of available commands. The output from `hub help`
does not conform to the same format or respect the `--all` flag.

To fix this issue, we only display hub's extended help when the
`--all` (or `-a`) flag is not present, falling back to git.