Link PEP references directly to PEP web pages in changelog.
Link PEP references directly to PEP web pages in changelog.

scoder/cython,da-woods/cython,cython/cython,cython/cython,da-woods/cython,scoder/cython,cython/cython,da-woods/cython,scoder/cython,da-woods/cython,scoder/cython,cython/cython