fix docstring of AddWithLimits
Merge pull request #2968 from zanzibar7/AddWithLimits_docstring

fix docstring of AddWithLimits
add nonpositive/nonnegative handling to Pow
fix test of evalf in facts
add I**im handling to assumptions
more general forms of tests and exp(i) and log(exp(i)) handling
add additional handling to old assumptions
add Examples text to docstring and shorten line
make Abs args canonical wrt sign
add symbolic mod handling so Mod(4*integer, 4) == 0
modify hyperexpand mod1 function
add new Min-replacement pattern to compute_cdf

If you don't do this you might get alternate results

https://travis-ci.org/smichr/sympy/jobs/19850479 shows the failure in
a run where 3 of the 4 python versions passed but one failed.