ENH provide a short-circuit for CSR/CSC/BSR sum_duplicates
FIX implementation of has_canonical_format (was is_canonical)
TST: add tests for in-place pchip derivatives

also use consistent naming for derivative order argument
DOC: mention pchip changes in the releases notes
Merge pull request #3331 from ev-br/pch

ENH: interpolate: more pchip changes

Add tests for in-place derivatives (which now work), mention the API changes in the release notes.
Merge pull request #3271 from jnothman/has_canonical_format

ENH: sparse: provide a short-circuit for CSR/CSC/BSR sum_duplicates

Parallel to has_sorted_indices, this provides is_canonical, allowing sum_duplicates to be avoided in repeated operations.
DOC: special: reformat special function ufunc docstrings + clean them up a bit
BUG: special: escape backslashes in docstrings
GEN: special: regenerate _ufuncs
Merge pull request #3332 from pv/special-docstr

DOC: clean up scipy.special docs