Add working classifier example
Update
Merge branch 'master' of github.com:chutsu/playground

Conflicts:
	docs/api/gp/tree.md
	docs/tree.md
	examples/classifier/classifier.py
	playground/gp/tree/__init__.py
	playground/gp/tree/evaluation.py
	playground/gp/tree/generator.py
	playground/gp/tree/mutation.py
	tests/gp/tree/crossover_tests.py
	tests/gp/tree/editor_tests.py
	tests/gp/tree/evaluation_2_tests.py
	tests/gp/tree/evaluation_tests.py
	tests/gp/tree/mutation_tests.py
	tests/gp/tree/parser_tests.py
	tests/gp/tree/tree_tests.py