spout new Field "the isPCM_SIGNED".

Signed-off-by: samueldeng <mr.dengshuoling@gmail.com>
get the filed isPCM_SIGNED from tuple.
finish user-defined function's JavaDoc.
clear the magic number. MAX_VALUE_*Bit.


Signed-off-by: samueldeng <mr.dengshuoling@gmail.com>