Pluginfy .zshrc
Add tig c(copy commit id) and o(open commit in browser) shortcut
Enable merge diff in tig's view-diff

This commit requires tig to consider %(diffargs) only in view-diff.
To do it, apply https://github.com/yasuoza/tig/commit/120f9fec148d150aed17fbc756111ee2964f67e3.patch