MAINT Include test folder in wheels

[rth]

Because the test folder didn't have an __init__.py file it was not considered to be a python module and was not included in wheels.

This adds it, which would make running tests on wheels easier in #150 with,

pytest --pyargs tslearn

this will run tests on the installed version of tslearn (installed from wheels or by other means).

[codecov-io]

Codecov Report

Merging #154 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
+ Coverage   93.86%   93.87%   +<.01%     
==========================================
  Files          22       22              
  Lines        2576     2579       +3     
==========================================
+ Hits         2418     2421       +3     
  Misses        158      158

Impacted Files	Coverage Δ
tslearn/__init__.py	75% <100%> (ø)	⬆️
tslearn/tests/test_estimators.py	94.87% <100%> (ø)	⬆️
tslearn/tests/test_shapelets.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6ae9112...2e82ae2. Read the comment docs.

[rth]

Also added a minor change to skip shapelets tests if keras or tensforflow are not installed,

python -m pytest tslearn/tests/test_shapelets.py -v
============================================================= test session starts =============================================================
platform linux -- Python 3.6.9, pytest-5.2.0, py-1.8.0, pluggy-0.13.0 -- /home/rth/src/tslearn/tslearn-env/bin/python
cachedir: .pytest_cache
rootdir: /home/rth/src/tslearn, inifile: setup.cfg
collected 2 items                                                                                                                             

tslearn/tests/test_shapelets.py::test_shapelets SKIPPED                                                                                 [ 50%]
tslearn/tests/test_shapelets.py::test_serializable_shapelets SKIPPED                                                                    [100%]

============================================================= 2 skipped in 0.77s ==============================================================

[rtavenar]

Can you also change tslearn version to 0.2.4 so that we use this version in our tests once merged ?