Use instance methods to DRY things up, and fix a bug discovered in
caskroom/homebrew-cask#26067 where Casks with language blocks would
always fail audit.

fixes 2 issues: error when username has a number, correct url for repos not on github

Handle the case when an argument passed to `brew cask` is both the name
of a Cask and a non-Cask file in the current working directory.

Fixes https://github.com/caskroom/homebrew-cask/issues/25611.

There is an existing `SystemCommand.run` that executes command with
`sudo`.  Use that instead of yet another custom wrapper.

In case the parent directory of Caskroom is writable for the user, we
don't need to use `sudo` to execute commands.

Make a generic method to run commands that has an option to switch sudo
so that we can run commands with and without sudo.

The homebrew/homebrew wiki no longer exists.

Relatively old code in Hbc::Caskroom recursively changes the ownership
of the directory where the Caskroom directory exists, that changes
entire files in /usr/local to user:staff if Homebrew setup with default
configuration.
This is really dangerous because it's easy to trigger (just simply type
`brew cask something` by following some installation documentation.)

This patch removes entire `chown` with -R option and make the logic
simply creating Caskroom directory with default Homebrew directories
ownership and permission.