Make use of test set on compute_perf optional; Update docs

This MR addresses two issues:

* Users which don't have a test set can now also use `bob_compute_perf`. In this case, only reduced number of statistics and plots are printed
* Fixes to the user guide, mainly concerning how to call the scripts since the simplifications with docopt

See merge request !22

Fixes verbosity; Fixes CMC plot (closes #20)

See merge request !21

Resolve "load_scores extremely memory hungry"

Closes #19 

Currently I left the old functions to read scores inside, but it might be a good idea to remove them and base everything on iterators. What do you think?

See merge request !20

[Automatic] update links and the ci mostly



See merge request !18

[Automatic] update links and the ci mostly



See merge request !17

Add score distributions on compute_perf (implementation similar to @akomaty's) - closes #15



See merge request !16

Docfix

This fixes include migrating from argparse to docopt and huge simplifications on the command-lines for each application.

It closes #16.

See merge request !15