Cache size data by commit hash, and enable direct commit comparison via CLI

[ItsNickBarry]

Example usage: hh size-contracts --compare 103541870332c9fb9125fad3684fcee613f13960

[ItsNickBarry]

Another possibility would be "named" outputs. Multiple such outputs could be cached.

For example:

hh size-contracts --name asdf
# later...
hh size --compare asdf

Using --compare with a git commit hash could still work here (as long as nobody uses a git commit hash as a --name).

[ItsNickBarry]

Make --compare a variadic argument, so that it works like git diff:

• no arguments compares uncommitted changes to current commit
• 1 argument compares uncommitted changes to given reference
• 2 arguments compares 2 references