-Changed getCO2 to return a char and if sensor is non existent will return NULL
-Changed getPM2 to return a char and if sensor is non existent will return NULL
-Added a new function getPM2_Raw which will return the value of PM2 as an integer
-Added a new function getCO2_Raw which will return the value of CO2 as an integer
-Added 2 new variables in the TMP_Raw Struct:
1. t_Char
2. rh_Char
These variables will be used to store the corresponding values as char and if sensor is nonexistent should be NULL
