Add functionality to install a certain tag/version number

[martinbeentjes]

I like the way tpm works, but I actually miss the option to add a certain tag or version number. Currently one can add a plugin by set -g @plugin 'tmux-plugins/tmux-sensible' for example. I think it seems like a nice feature to add support of installing a certain version by:

set -g @plugin 'tmux-plugins/tmux-sensible'@v3.0.0

And such that tpm will recognize the version number, parse it to the correct URL representation and git clone that certain version.