Fxpmath

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* right shift support expand shifting='expand' mode.
* improve performance in indexed assignement.
* Fxp slicing (when Fxp has values as array) returns a Fxp object.
* Fxp accept other Fxp as input value.
* New `sum` function in `functions`.
* Fxp object supports > 64 bits words and values.
* docstrings update.

Thanks following users for their feedback:
lpuglia, MaenMallah, FredKellerman

* chage in setup.py to resolve not installed package dependencies. Thanks to jcharlong .

* fix wrap error for ndarrays.

Thanks to **lpuglia**

* fix wrap error for unsigned Fxp.

Thanks to **lpuglia**

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* fix shifting bitwise of unsigned values.
* fix wrap error when input was a float.

fix bug of N (N > 1) dimensional arrays as inputs.