[MRG] Documentation for carl.learning

[glouppe]

• Unified interface for calibrators (fix Unify calibrators under a common interface #37)
• Documentation of carl.learning.base
• Documentation of carl.learning.calibration
• Documentation of carl.learning.parameterize

[glouppe]

Merging this, carl.learning is now fully documented. I'll now proceed to generate the static documentation, now that the documentation is there for at least one module.

[cranmer]

+1