Add .gitignore.
Implement histogram filling.
Allow configuration of number or events processed.
Reorganize code.  Also add plotting stub (unable to disentangle).
Fix CSV related flags.
Load processes the right way.
Implement basic stack plotting.  Systematics still left to do.
Fix the copy constructor and addition of Processes.
Fix legend top margin.
Fix flag handling.
Add training and booking of MVAs.
Ignore compiled python files.
Fix process expansion when processing.
Revamp combining of processes and update list of combined processes.
Improve stacking;  Reverse stack order, fix ratio plots.
Clean up a bit.
Update config to a more recent analysis version.
Update flags.
Update the way branches are handled.

For now, the script `setup_branches` takes a ROOT file and updates the source
with new branch variables, where weights are stored in the superclass.
Fix plotting a tad bit.