BF: boost min cython to 0.23

[yarikoptic]

closes #14699
closes #14508

[jreback]

prob need to change a few travis setups in ci
for this to work

[yarikoptic]

what is btw really the lowest version of cython which works in your setups and passes the tests? 0.23 here is somewhat arbitrary one higher than 0.21.1 where 14699 manifested

[codecov-io]

Current coverage is 85.26% (diff: 100%)

Merging #14831 into master will not change coverage

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[jreback]

ci/install_travis.sh:    pip install cython==0.19.1
ci/requirements-2.7.build:cython=0.19.1
ci/requirements-2.7_COMPAT.build:cython=0.19.1
ci/requirements-2.7_LOCALE.build:cython=0.19.1

[jreback]

@yarikoptic I think 0.23 is fine. if you can add a note on 0.20.0 whatsnew. also need to update install.rst I think (as well as change those files I listed above).

[yarikoptic]

interesting -- now 2nd env in travis fails due to failing to find pandas/index.c any immediate clue why?

[jorisvandenbossche]

@yarikoptic that build is still installing cython 0.19.1 (see the requirements-2.7_LOCALE.build file), so it acts like cython is not installed (I only thought we had a better error message for such cases)

[jorisvandenbossche]

LGTM

@jreback

[jreback]

seem some files have no changes?

can you add a note in the whatsnew 0.20.0 (in addition to the one you have), about the development requireing a higher version.

can you see if anything needs to be changed in contributing.rst

otherwise lgtm.

[yarikoptic]

@jreback

• "no changes" -- read between the lines ;) git would not have a change registered if there were no changes -- while at it fixed some permissions
• whatsnew entry was added a while back... now had to resolve merge conflict already. would appreciate a merge ;)

[jreback]

thank you sir!