Reduce test job time

[fukatani]

• cache dependency
• Reduce some version test (mainly appveyor)?
  Is it enable to omit python 3.5 and 3.6 test for appveyor?

[StrikerRUS]

@fukatani

Caching detail is here.
https://docs.travis-ci.com/user/caching/#Things-not-to-cache
https://www.appveyor.com/docs/build-cache/
I check test time, some library build and download time is not ignorable.
https://travis-ci.org/fukatani/rgf_python/jobs/324187850
conda
It tooks 200sec.
https://github.com/theochem/qcgrids/blob/ac5d1e263b8f3fe0e659f908ab8bc849970ec24f/.travis.yml#L46-L54
ccache
We can cache fast rgf builf. (about 1min.)
pip
Not effective. Only pytest is effective.
apt, brew
We cannot cache public repository.
travis-ci/travis-ci#5876
Since sometimes CI is failed by timeout of downloading g++, I want to cache g++. But I don't know how we can.

Yeah, I agree that downloading g++ is the most time expensive and risky thing. But caching it we are closing our project for new versions 😢 .
By testing all Python versions on all platforms we are able to catch small problems(not bugs). The first thing comes to my mind is recent problem with buggy version of mkl which comes only on Windows with Python 3.4.

To be honest, I'm not suffering from long tests now. Do you?

[fukatani]

If someone is allowed to wish so much, sometimes I want to CI result immidiately.
I will try if there is a good way.

[StrikerRUS]

Yeah! And every time bug-free code!.. 😃