Performance Improvement

* All: Changed to use `boost/timer/timer.hpp` instead of `boost/timer.hpp`, because it has been deprecated.
* Metadata: With the intent of performance improvement, optimized the process for equivalence determination against the following classes:
  * AssemblyGenerator/AssemblyMetadata
  * CustomAttributeMetadata
  * FieldMetadata
  * LocalGenerator/LocalMetadata
  * MetadataDispenser
  * MethodBodyGenerator/MethodBodyMetadata
  * MethodGenerator/MethodMetadata
  * ModuleGenerator/ModuleMetadata
  * ParameterMetadata
  * PropertyMetadata
  * TypeGenerator/TypeMetadata