Put an IRC link to README.
Replace IRC link with WebChat link

It seems GitHub doesn't allow irc:// protocol, so replace it with WebChat link.
Support iTerm2 forward/backward word escapes
(https://github.com/fish-shell/fish-shell/issues/920)
Adjust prefix completions to sort alphabetically instead of by length.
Other completions are still sorted by length.
https://github.com/fish-shell/fish-shell/issues/923
Try to improve the error message printed when libcurses is not found
Fix indentation
Fix more indentation in fish_default_key_bindings.fish
Merge remote-tracking branch 'upstream/master'