Thanks to Gernot Schulz for writing most of the new content. It somewhat overlaps with INSTALL, but more docs are better either way.

As this is non-destructive, people may prefer it

* Fixed issue where vcsh init & clone would print help as they
  tried to call currently non-existant vcsh use

* Has been tested on my and other's machines for months
* Includes zsh completion
* Does not support `vcsh use`, but in a releasable state otherwise

* This version should be fully POSIX shell compliant
* Quoted all variables withing [ ]
* Added debugging and verbose output via shell variables
* Cleaned up INSTALL

Switch from zsh to POSIX sh

All zsh-specific stuff will be done in a zsh function which will wrap vcsh.

No idea why

  [[ -n $ZSH_VERSION ]] && vcsh_exit() {vcsh exit; zle reset-prompt;}

errors out with

  vcsh: 96: Syntax error: "}" unexpected (expecting "fi")

but oh well.