Support debug/verbose mode

[desyncr]

As per https://trello.com/c/osZqPWKz/107-support-debug-verbose-mode

Support for:

> antigen bundle zsh-users/zsh-syntax-highlighting --debug
Gonna install 'https://github.com/zsh-users/zsh-syntax-highlighting.git'...
Clone OK: '$ADOTDIR/zsh-users/zsh-syntax-highlighting'
Determining entry point...
Found entry point: '$ADOTDIR/zsh-users/zsh-syntax-highlighting/zsh-syntax-highlighting.plugin.zsh' using dot-plugin strategy.
No entries found to add to PATH. Not updated.
No entries found to add to fpath. Not updated.
Record entry: 'https://github.com/zsh-users/zsh-syntax-highlighting.git|master / plugin true'

Support --debug and --dry-run.

[desyncr]

Should be fixed with #529. Maybe separated/extracted from that PR if it further delays deploying.