Adds complex math expressions support

[thepabloaguilar]

I've implemented the _MathExpression callable class to work with complex math expressions.
It accumulate the operations when the instance is called all the operations are reduced to get the final result!

Example:

>>> from lambdas import _MathExpression
>>> complex_expression = (10 ** 2) / _MathExpression() * 10
>>> complex_expression(2)
500.0

I've modified _Callable class too, to use the _MathExpression in its math operation and now we can use it normally, no side effects:

>>> from lambdas import _
>>> complex_expression = (10 ** 2) / _ * 10
>>> complex_expression(2)
500.0

---

TODO:

• Reach coverage 100% (in fact was 97% of all coverage, but 100% of my implementation)

closes #1

[thepabloaguilar]

@sobolevn I'm not sure about typing, could you take a look please?

[thepabloaguilar]

@sobolevn I've reached 97% of test coverage, because _fmap is never called and we don't have any tests for and, or, etc.
I opened #4 to convert all functions:

# FROM
class _Callable(object):
    __and__: Callable[['_Callable', T1], Callable[[T1], T1]] = _fmap(operator.and_)

# TO
class _Callable(object):
    def __and__(self, other: Any) -> Callable[['_Callable', T1], Callable[[T1], T1]]:
        return _fmap(operator.and_)

After the conversion we will have to write all the tests, I can write them after this PR!

[thepabloaguilar]

@sobolevn is something else needed?

[sobolevn]

Thanks a lot!