Add a BridJ annotation field to ConvertedType

This will be useful for mapping types with no direct equivalent
in Java, like size_t to @Ptr long, or glong to @CLong long.
Add the beginnings of method generation

Pretty wrappers that present @Ptr longs as Pointer<Something>s are
not yet generated, and varargs parameters are not parsed explicitly
through the <varargs /> element. There also seems to be a type mapping
bug that is unrelated to method generation. But, it looks good for a
start.
Add the source XML to every generated method as comment

This is to make checking and debugging easier. The idea comes from
JNAerator.