Add a stats sub-command

[nikoksr]

Is your feature request related to a problem? Please describe.
It would be very interesting to see how much time and how many keystrokes you saved by using proji.

Describe the solution you'd like
Something like a proji stats command or something like this might be a quick way to check your all time stats.

Additional context
Saved keystrokes would be relatively easy to calculate. For saved time we might use the global average keyboard typing speed as a reference.
Only problem is that I don't want to calculate these stats after every time a new project got created. Project creation should be as quick and clean as possible. That's what it's about.
The solution might be to take all (active & dead) projects from storage and calculate their total statistics in terms of saved timed and keystrokes. The downside is purging. If the user purges the projects database regularly, soft-deleted projects will be finally deleted which leads to incomplete statistics.
Maybe projects shouldn't be purge-able? We'll see.