Several NetSubscription changes...

Remove Cased data type - not relevant to this module.
Add current UpdateRef, SubRef and SessionRef to Handler data type.
Add new{Update,Sub,Session}Ref functions that return a new ref and increment the current within the Handler.
doByteRead and doByteWrite now throw errors - these errors are thrown for even trivial or expected issues. This method allows us to handle the issue elsewhere.
Remove IO portion from doByteWrite and doByteWrite, these will be done elsewhere.
Add WriteError and ReadError data types. These will be the errors encountered from doByteWrite and doByteRead.