Fix a bug causeing `gist -c` fails for xsel users.

Unlike `xclip`, calling `xsel` without any argument outputs the
selection.
In other words, `xclip` defaults to `xclip -i`,
but xsel` defaults to `xsel -o`.

Thus we should use `xsel -i` instead of `xsel` for copying the url
to clipboard.
Merge branch 'master' of github.com:weakish/gist
bump version
Remove JSON dependency [Fixes #152]
add Gist#rawify

for anonymous users, the url returns from gist api is something like
https://gist.github.com/7216441 , and it would redirect to
https://gist.github.com/anonymous/7216441, it's not easy to get
the raw file url by scripting.

this commit make the hack to handle the HTTPRedirection, and concate
the result url with /raw to generate the raw url.
add -r option, and allow use combination with -s
add spec for Gist#rawify
modify -r to -R

gist may support recursively gist all files in a directory by `-r`
add comment for rawify