New theme: change path face for git subdirs, display time

[Ambrevar]

My eshell theme has 2 features which I believe are not part of eshell-prompt extras:

• The subdirs of a git repository are colored with a different face. This makes it obvious in which Git repo we are. It's "gnu/packages" in the screenshot.

• For every command that takes more than 1s to complete, display the duration and date once it's completed. I find this very useful since there is no need to think in advance whether we should call time or not. Plus it gives a timestamp of of termination of all long commands.

I can send a patch if you are interested.

[xuchunyang]

Sounds like useful features, although I don't use this package (nowadays I prefer a minimal prompt), if you send a patch, I will test and merge it.