Itchy is nearly all new code

It's no longer recognizable as what I forked it from. Maintain
attribution for the original and keep the license, but update all
references to my fork.

Bump version to 1.0.0
Make autoload

Move functions to autoload. Increment version to 2.0

new_buffer is the only function used in the API, so all the rest can
stay as script-local functions.

s:unscratch is called from a command, but I confirmed that it still
works (the command is defined within a function in the same file).