The chunks of types in excluded_chunk_types will not be counted in
ChunkEvaluator. This is useful for tasks such as SRL, in which chunks of
type V (verb) will not be taken into account in evaluation.

In order to keep consistent with other evaluators, an extra parameter
label is add to chunk_evaluator. Document and demos are modified
accordingly.

* remove unnecessary field set in ParameterConfig, Evaluators, etc

* Add some comments for CTC layer and fix CTC evalutors, also add interface test

ISSUE=4584581 

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1413 1ad973e4-5ce8-4261-8a94-b56d1f490c56

ISSUE=4586495

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1408 1ad973e4-5ce8-4261-8a94-b56d1f490c56