Fixed the single-letter alias within a path bug
Increased version to 2.13
Added the patter Bin/*.dll.mdb to .gitignore
Added a test class to start testing Polymorphic Serialization, a workaround to get rid of yax:realtype attribute
Defined two attributes [YAXCollectionItemType] and [YAXType]
Updated unit tests so that they pass regardless of .NET Framework version