Rotuine name: kjt_get_envar

Action: gets (address of) value of an environment variable

Input Registers : HL = name of variable (4 chars max, zero-termination required if less than 4 chars)
		
Output Registers: If zero Flag = Set : all OK,  HL = address of data for variable (4 bytes)
                  If Zero Flag = Not set: variable was not found, HL = address of envar list, A = max entries