A new configuration property 'collect-errors' was added to the beanmapping.xsd for #88.

The documentation in beanmapping.xsd is updated. All XML-Parser and configuration related Java classes are also updated so that the new configuration property can be read.
Updated the documentation of beanmappings.xsd and the fluent interface of DozerBuilder.MappingBuilder for the new configuration property 'collect-errors'.
Modified the MappingProcessor so that it can collect the errors if the 'collect-errors' flag is set to true #88.

Added a new exception CompositeMappingException which will be thrown at the end of the mapping if the 'collect-errors' flag is set to true.
Added a unit test CollectErrorsTest to test the above changes.
In MappingProcessor, the logic about allowed exceptions is partially moved to MappingUtils to reduce redundant code.