Allow slash in buffer name

[cole-brown]

I have buffer names like:

• impatient-mode:/…/README.md
• emacs:/…/unique/path/file.el
• emacs:/…/also/file.el

These buffers could not be displayed by impatient-mode due to how the buffer name was passed around in the URL. This fixes the encoding/decoding/parsing of the URL to allow for such buffer names.

[liuyinz]

Thanks to your fix ! I think https://github.com/skeeto/impatient-mode/issues/18 is related to this bug. @skeeto