Update GPRS_Shield_Arduino.h

Add isSMSunread and readSMS (with more information) functions.
Version 0.4

Add isSMSunread and readSMS (with more information) functions.
version 0.6

Add isSMSunread and readSMS (with more information)
Also some detected bugs in readSMS and deleteSMS
version 0.1

Example how to use isSMSunread and readSMS (with more information)
version 0.1
version 0.1
Delete GPRS_SMSread.ino
Add GPRS_SMSread.ino example

Add GPRS_SMSread.ino example
Merge pull request #3 from op2op2op2/master

Add isSMSunread and readSMS (with more information) functions, some bugs also detected