[feat] Support statistics print by adding results manager object (#334)

* [feat] Support statistics print by adding results manager object

* [refactor] Make SearchResults extract run_history at __init__

Since the search results should not be kept in eternally,
I made this class to take run_history in __init__ so that
we can implicitly call extraction inside.
From this change, the call of extraction from outside is not recommended.
However, you can still call it from outside and to prevent mixup of
the environment, self.clear() will be called.

* [fix] Separate those changes into PR#336

* [fix] Fix so that test_loss includes all the metrics

* [enhance] Strengthen the test for sprint and SearchResults

* [fix] Fix an issue in documentation

* [enhance] Increase the coverage

* [refactor] Separate the test for results_manager to organize the structure

* [test] Add the test for get_incumbent_Result

* [test] Remove the previous test_get_incumbent and see the coverage

* [fix] [test] Fix reversion of metric and strengthen the test cases

* [fix] Fix flake8 issues and increase coverage

* [fix] Address Ravin's comments

* [enhance] Increase the coverage

* [fix] Fix a flake8 issu

Author: nabenabe0928

examples/40_advanced/example_resampling_strategy.py

@@ -93,7 +93,7 @@
 
 ############################################################################
 # Search for an ensemble of machine learning algorithms
-# -----------------------------------------------------------------------
+# -----------------------------------------------------
 
 api.search(
     X_train=X_train,
@@ -107,7 +107,7 @@
 
 ############################################################################
 # Print the final ensemble performance
-# ------------
+# ------------------------------------
 y_pred = api.predict(X_test)
 score = api.score(y_pred, y_test)
 print(score)