DOC: the type of `exact` parameter
`comb` support combinations with repetition
add tests for comb
add `perm` function
add tests for `perm`
fix tests fail
some cleanup
fix tests fail
move comb and perm to scipy.special
use special.binom to compute comb
add more tests
remove perm from scipy.misc
special: fix perm/comb scalar case
Merge pull request #3097 from branch pr/3097

ENH: special: Add `perm` function and support for combinations with repetition

This PR add a perm function, which computes the number of k-combinations
of n, into scipy.special.  It also adds the support for combinations
with repetition to comb function, and moves the implementation to
scipy.special