New static and factory creators.

Added `AbstractLoomFactory` and `LoomFactory` as creators for the Loom object.
Moved `Loom->diff()` into the `LoomComparisons` trait.
Added a `daysPerMonth` parameter to `Loom->getMonths()` and to `LoomFactory->fromMonths()`
The `Months->__construct()` will also accept a `daysPerMonth` parameter.
Added a static `make()` method to the `Loom` object which returns a new instance of `LoomFactory`.
update badges
Updated badges.
show `dev-develop` build status in `readme.md`.
Basic arithmetic feature.
Added a `sub()` and `add()` method to the `Loom` object. Both methods accept a `Loom` object as a parameter.
Merge branch 'develop'

Conflicts:
	readme.md