Refactor robosat to be a proper library with utility tools on top of it

At the moment we almost have a clean split in place: we have command line utilities in robosat.tools and everything else split off of it. What we should do is making sure all functionality is in packages and not in robosat.tools: all the command line tools should do is parse command line arguments and then delegate to robosat library functions.

Here are an examples where this is not the case currently:

• The convert tool has the functionality for splitting off masks
• And the masks tool has the functionality to do the soft-voting

These features should be encapsulated in robosat packages and then only getting called in the tools.

Why are we doing this? We want to create a Python robosat package folks can install and re-use. Think:

pip install robosat

from robosat.ensemble import softvote
....

Our tools should have a dependency on this robosat package; but not the other way around.

Start by inspecting the robosat.tools command-line utilities, especially convert and masks, and identify functionality that belongs in robosat packages. Move mask splitting and soft-voting behind reusable library entry points, then verify that the tools only parse arguments and delegate to them. Done means the robosat package can be installed and imported independently of the tools.