CLN: Use timezone natively supported by pytz

Apparently Asia/Beijing is actually used in China, but it's
not natively supported in timezone software. See for example:
https://bugs.launchpad.net/ubuntu/+source/libgweather/+bug/228554

That said, example timezone in docs should at least work, so
that's the reason for the change
CLN: Make aware vs. naive always a TypeError
CLN: Clean up the _cached_range exceptions and checks

(Plus catch the uncaught obj + None TypeError that was going on in the
test cases)
Merge branch 'googlenetwork' of https://github.com/gliptak/pandas into gliptak-googlenetwork
DOC: edit release notes
Merge pull request #3955 from jtratner/makefile-updates

BLD: Tweak to Makefile.
BUG/BLD: add compiler flag for older compilers

The -D_GNU_SOURCE is needed by older versions of GCC. Many newer versions
enable this flag by default, which is why it wasn't being caught before.
Merge pull request #3959 from cpcloud/ujson-cmplr-flag-fix

BUG/BLD: add compiler flag for older compilers
Merge pull request #3956 from jtratner/change-bare-exceptions-1

CLN: Change bare exceptions pt 1
CLN/DOC: convert GH* issue mentions to the extlinks version
ENH add cython tutorial
FIX add cython to toctree
CLN/DOC: move release notes to docs
CLN: remove ability to refer to pull requests by sphinx roles
CLN/DOC: change links to release notes in CONTRIBUTING and whatnews
CLN: remove :hidden: and change release to markdown
Merge pull request #3961 from cpcloud/github-issue-sphinxext

DOC/CLN: remove gh links and use the new issue format for whatsnew
CLN: fix grammar in extract_index error message
TST: update test to reflect error message change
Merge pull request #3972 from cpcloud/fix-error-msg

CLN: fix grammar in extract_index error message