verbose update logs

[AdrienLemaire]

Currently, tpm will show this message every time I execute ctrl-b-U, then type 'all':

Updating all plugins!                                                                                                                                                                                           [0/0]  "tmux-sensible" update success
  "tmux-open" update success
  "tmux-urlview" update success
  "tmux-continuum" update success
  "tpm" update success
  "tmux-copycat" update success
  "tmux-resurrect" update success
  "tmux-yank" update success
TMUX environment reloaded.
Done, press ENTER to continue.

All packages always show 'update success', whether they really updated or not.

I would like to see more useful information:

• Only list packages that have really been updated
• show the from -> to commits/tags to understand how the package has been updated
• bonus: show the changelog url, so that I can jump to it and read what was added/removed/deprecated in that plugin (I don't mind manually adding urls in a config file once).

[Alkindi42]

Hello, I created a PR (#179) to improve the situation. Do not hesitate to participate.