Stacked Git 2.0.0-rc.2

This second 2.0 release candidate repairs several bugs and refines how git options are passed-through in stg diff, stg show, and stg email commands.

Changed

• The --diff-opts option is renamed to --diff-opt. --diff-opts remains available as an alias.
• The --diff-opt option no longer allows multiple git options per occurrence. This allows git diff options with spaces in their values.
• The --git-opts option for stg email format and stg email send is renamed --git-opt.
• The --git-opt option no longer allows multiple git options per occurrence. This allows git options with spaces in their values.
• Zsh completion for --diff-opt and --git-opt leverage the full-featured git completion capability.

Fixed

• Repair check for modifications to stack by external tools.
• stg pull and stg rebase record updated stack state instead of deferring until the next stack-modifying command to do so.
• Improve patch appliction with git apply --3way when pushing` (#225)
• Zsh completion for --diff-opt accommodates multiple occurrences