Add man pages search

- since alfred is mac only, i guess it's reasonable to use apple man pages

- update is pretty expensive (data json is sized about 1.5mb) so I didn't use auto updater, and the man pages don't update that frequently anyway

- will upload the external update code to a repo soon

- alfred seems to have messed up info.plist(I simply added a script filter, no other things modified), not sure how it happened, sorry about that.

- I wanted to add description to each command, but that means requesting all individual  man pages (should take a very long time) and parse out the description text(usually just text behind `--` in the `NAME` section, but with variations). gave up eventually.

- thanks for sharing this great workflow :)