Major performance improvements and minor bug fix

+ Added excellent and efficient way of sending packages without a
specific thread, based on old thread-sending code;
> Improved package header to/from byte array conversion - is now 6 times
faster;
> Fixed very rare exceptional case in heartbeat bouncing and sending;
> No longer throwing unconventional exception in Dispose methods;
> Fixed request disposal to do what it should do and other disposal
methods.

vProto.Packages.PackageHeader structure is now unsafe and includes an
internal array over its whole memory space. A handy property is used to
"unsafely" convert the structure to/from a byte array by fixing and
incrementing pointers. This method was benchmarked and is 5-7 times
faster than the old marshalling code.