textproc/py-markdown: Update to 2.6.5

• Update PORTVERSION and distinfo checksum (2.6.5)
• Update test dependencies and test target
• Remove dos2unix, no longer needed
• Enable architecture independence (NO_ARCH)
• Backport upstream issue 453 [1] fix for failing tests due to pygments
• Patch setup.py to support setuptools test command
• Update pkg-descr WWW: URL (matching that in setup.py)

[1] https://github.com/waylan/Python-Markdown/issues/453

Requested by: brnrd (via IRC)