modified AmfArray,AmfValue test cases

Change point:

・Mntone.Data.Amf
 1.added COMExceptionHelper class
 2.modified AmfArray class
 3.modified AmfValue class

・Mntone.Data.Amf.UnitTest
 1.added AmfValue's some test cases
 2.modified AmfArray's test cases
 3.modified AssertHelper class