Change signature of 'readFromMaster()'

Change signature of 'readFromMaster()' to take destination buffer for
parameter along with the size of the buffer
Correct description of 'readFromMaster()'

System will return failure code '-1' if there is no data to read.
Therefore 'readFromMaster()' can't distinguish no-data-to-read from
other failures (whatever they may be).
Correct planned functionality for 'readFromMaster()'

It's read from "Master" not "Client" in this interface
'readFromMaster()' return error if passed null ...

... and return zero if passed destination buffer of size zero
'readFromMaster()' fail if read fails ...

... and return the number of read characters if successful
'readFromClient()' destination buffer as parameter
'readFromMaster()' pass buf to 'readFromClient()'

'readFromMaster()' pass destination buffer to 'readFromClient()'