Use stopit module for timeout function

[weixuanfu]

What does this PR do?

1. Remove Interruptable_cross_val_score class since it cannot stop thread cleanly.

2. stopit module can raise a Exception in a working thread for stopping thread and has a better decorator for timeout function

3. Because Ctrl + C works with n_jobs is not 1 in Windows OS after usingstopit module, the related warning message was removed

Where should the reviewer start?

gp_deap.py

How should this PR be tested?

Any TPOT examples

What are the relevant issues?

#508

Questions:

• Do the docs need to be updated? Yes, updated in the PR
• Does this PR add new (Python) dependencies? Yes, need stopit module

[coveralls]

Coverage decreased (-0.1%) to 86.922% when pulling 03eed0d on weixuanfu2016:stopit into 7f2b6a7 on rhiever:development.

[weixuanfu]

Update:

After more tests, freezing issue #436 and #422 are also fixed somehow in Windows OS (~6s/pipeline) using test codes below. But for Linux OS, it is ~22s/pipeline.

# coding: utf-8
from sklearn.datasets import make_classification
from tpot import TPOTClassifier
# make a huge dataset
X, y = make_classification(n_samples=50000, n_features=200,
                                    n_informative=20, n_redundant=20,
                                    n_classes=5, random_state=42)

# max_eval_time_mins=0.1 means 6 seconds limits for evaluating a single pipeline 
tpot = TPOTClassifier(generations=5, population_size=50, offspring_size=100, random_state=42, n_jobs=1, max_eval_time_mins=0.1, verbosity=3) 
tpot.fit(X, y)

[rhiever]

Future note (also to @teaearlgraycold): Please don't rebuild the docs in future PRs. That's an easy way to get ugly merge conflicts.

[weixuanfu]

OK, I will restore changes in docs.

[weixuanfu]

Changes in docs was reverted.

[coveralls]

Coverage decreased (-0.1%) to 86.922% when pulling e27059b on weixuanfu2016:stopit into 7f2b6a7 on rhiever:development.