Add CURL support

[sharkdp]

... so we can do things like

bat https://raw.githubusercontent.com/sharkdp/bat/master/src/main.rs

or just do it the UNIX way 😄

curl https://raw.githubusercontent.com/sharkdp/bat/master/src/main.rs | bat

Both cases would probably require us to infer the programming language from the file contents.

[sharkdp]

Closing this, as we can now easily do this via:

curl -s https://raw.githubusercontent.com/sharkdp/bat/master/src/main.rs | bat -l rs