* gradient_clipping_threshold should be allowed to set with parameter-grain

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.

* math => layer_math
* Fix #903

* Partially fix #622

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

These three parameters have already been moved to model_average. Leaving
them here will cause duplicate keys in kwargs

test_rest_hook.py => test_reset_hook.py

Change-Id: I84909ade4a1ea2bec4311264626dd000cd6bc86c

To solve this, we maintain the list of DefaultNameFactory used in by trainer_config_helper,
and reset the state at the beginning of each parse_config call.

Change-Id: I13c7574dc8f0b6bc6f6b7c92eb425e2c52c926e8

Added a test in test_NetworkCompare to verify cudnn and exconv, fixed a bug in cudnn_conv in dealing with groups

* Make float equal works well.
  * compare 0.01 and 0.009999999999 will return true.

Change-Id: Ic80845c892c96c37a0df0ddc433fe1aeaa5a9d1c

out = w * input
where w is a parameter of size 1

Change-Id: Ife682d62323ceb1a20cbbf6269421b20a862d888