refactor + new features (conditional, repeated sink paths, collection source, generator settings)

[bulricht]

implements #52

[github-actions]

Tests coverage table for d93e00c commit.

Name	Stmts	Miss	Cover	Missing
pysubyt/api.py	138	3	97.83%	159 351 355
pysubyt/j2/generator.py	17	0	100.0%
pysubyt/sinks.py	90	13	85.56%	19 33-34 38 42 55 58 61 64 67 77 80 113
pysubyt/sources.py	215	22	89.77%	26 70-77 92-93 125 240 245-246 277 288 291-292 323 330
pysubyt/subyt.py	18	0	100.0%
TOTAL	478	38	92.05%

[cedricdcc]

Perhaps this should be open science vliz

[cedricdcc]

Should we have a convention stating that we limit ourselves to the latest mayor version of a package eg: 4.x.x ? This to prevent later failures with other library implementations.

[jorgecunhamendes]

I removed myself as a reviewer since I don't think I can provide any meaningful review at this point. I may have some ideas for the testing part, which falls a bit outside the context of this PR, I think.