Add generic rising_factorial and rising_factorial2

[fingolfin]

No description provided.

[codecov]

Codecov Report

Merging #1445 (ea0e065) into master (7ba6303) will increase coverage by 0.00%.
Report is 2 commits behind head on master.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1445   +/-   ##
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  Coverage   84.60%   84.60%           
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  Files         109      109           
  Lines       29361    29370    +9     
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+ Hits        24841    24849    +8     
- Misses       4520     4521    +1     

Files Changed	Coverage Δ
src/AbstractAlgebra.jl	56.25% <ø> (ø)
src/generic/Misc/Rings.jl	36.00% <100.00%> (+36.00%)	⬆️

... and 9 files with indirect coverage changes

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[fingolfin]

Note that Nemo already has specialized methods for rising_factorial and rising_factorial2 so this may be breaking for that reason (i.e., import/export shuffling).

But the implementations there are only for numbers; but this is also useful for e.g. polynomials. And rising_factorial2 in Nemo is only available for arb/RealFieldElem/acb/ComplexFieldElem, but not for e.g. integers.

[thofma]

Looks good, but doctests are failing.

[fingolfin]

Fixed now