Add support for URLs as -p option values.

Try to download any patches specified via the -p option that start with
http or https and apply them.

So this example from README really works:

$ ruby-install -p https://raw.github.com/gist/4136373/falcon-gc.diff ruby 1.9.3-p429
Merge pull request #61 from bkutil/remote_patches

Add support for URLs as -p option values.
Should be an Array.
Set SRC_DIR and RUBY_SRC_DIR to use test/src/.
Avoid wordsplitting and path expansion of $PATCHES. (@zendeavor)
More quoting.
Swap path/patch variables.
Inline.
Spacing.
Download the patches into $SRC_DIR/$RUBY_SRC_DIR.
Split tests into two files.
Version bump to 0.3.0.
Added the --mirror option.
Updated the man pages
Forgot to add -M,--mirror to the usage.
Updated the ChangeLog for 0.3.0.
Give credit where credit is due.
Added examples of using the -M and -p options.
Updated the README.
Bumped the versions in the README.