Revamp fish completion
Revamp fish completion

The fish completion hadn't been updated since 2009; this brings it up
to date. Changes include:

* Create the list of commands the same way as in bash completion
* Add every option for every current command, with descriptions
* Fixes a bug in fish_complete_brew_command
* Allow fish_complete_brew_command to take multiple commands
* Expand functionality of fish_complete_homebrew_formula to support
  other commands and taps, and change name to reflect new functionality

Tested on fishfish, but should be compatible with fish.

mgrimes/brew,claui/brew,EricFromCanada/brew,DomT4/brew,aw1621107/brew,palxex/brew,nandub/brew,maxim-belkin/brew,jmsundar/brew,staticfloat/brew,MikeMcQuaid/brew,muellermartin/dist,jmsundar/brew,nandub/brew,alyssais/brew,reelsense/brew,aw1621107/brew,claui/brew,sjackman/homebrew,Homebrew/brew,alyssais/brew,reitermarkus/brew,mistydemeo/homebrew,MikeMcQuaid/brew,ilovezfs/brew,rwhogg/brew,jmsundar/brew,MikeMcQuaid/brew,aw1621107/brew,amar-laksh/brew_sudo,rwhogg/brew,konqui/brew,Linuxbrew/brew,MikeMcQuaid/brew,sjackman/homebrew,gordonmcshane/homebrew,palxex/brew,konqui/brew,amar-laksh/brew_sudo,muellermartin/dist,konqui/brew,reitermarkus/brew,alyssais/brew,vitorgalvao/brew,vitorgalvao/brew,hanxue/linuxbrew,zmwangx/brew,hanxue/linuxbrew,mgrimes/brew,nandub/brew,staticfloat/brew,sjackman/homebrew,DomT4/brew,zmwangx/brew,mgrimes/brew,reelsense/brew,bfontaine/brew,toonetown/homebrew,reitermarkus/brew,amar-laksh/brew_sudo,pseudocody/brew,mahori/brew,rwhogg/brew,EricFromCanada/brew,bfontaine/brew,JCount/brew,pseudocody/brew,Homebrew/brew,palxex/brew,staticfloat/brew,JCount/brew,EricFromCanada/brew,JCount/brew,DomT4/brew,mahori/brew,ilovezfs/brew,Linuxbrew/brew,tonyg/homebrew,toonetown/homebrew,konqui/brew,mistydemeo/homebrew,sjackman/homebrew,vitorgalvao/brew,Linuxbrew/brew,EricFromCanada/brew,mahori/brew,pseudocody/brew,DomT4/brew,Linuxbrew/brew,ilovezfs/brew,reelsense/brew,AnastasiaSulyagina/brew,AnastasiaSulyagina/brew,gregory-nisbet/brew,AnastasiaSulyagina/brew,Homebrew/brew,maxim-belkin/brew,mahori/brew,toonetown/homebrew,gregory-nisbet/brew,muellermartin/dist,bfontaine/brew,reitermarkus/brew,maxim-belkin/brew,vitorgalvao/brew,tonyg/homebrew,gregory-nisbet/brew,gordonmcshane/homebrew,nandub/brew,claui/brew,JCount/brew,Homebrew/brew,mistydemeo/homebrew,zmwangx/brew,claui/brew,hanxue/linuxbrew,tonyg/homebrew,gordonmcshane/homebrew