Adds sleep-support to command struct

It is cleaner to store the needed wait-time with the struct than to
passit to the read-write function. This change mostly acopmplieshs that

sgptest.py

@@ -14,21 +14,27 @@ DEVICE_ADDR = 0x58
 #print bus.write_byte_datadata(DEVICE_ADDR, 0x00, 0x01)
 #self._i2c_read_words_from_cmd([0x36, 0x82], 0.01, 3)
 
-Sgp30Cmd = namedtuple("Sgp30Cmd",["commands","replylen"])
-GET_SERIAL=Sgp30Cmd([0x36, 0x82],6)
-GET_FEATURES=Sgp30Cmd([0x20, 0x2f],2)
-IAQ_INIT=Sgp30Cmd([0x20, 0x03],0)
-IAQ_MEASURE=Sgp30Cmd([0x20, 0x08],6)
-IAQ_SELFTEST=Sgp30Cmd([0x20, 0x32],3)
+Sgp30Cmd = namedtuple("Sgp30Cmd",["commands","replylen","waittime"])
+GET_SERIAL=Sgp30Cmd([0x36, 0x82],6,10)
+GET_FEATURES=Sgp30Cmd([0x20, 0x15],2,2)
+IAQ_INIT=Sgp30Cmd([0x20, 0x03],0,10)
+IAQ_MEASURE=Sgp30Cmd([0x20, 0x08],6,12)
+IAQ_SELFTEST=Sgp30Cmd([0x20, 0x32],3,520)
+GET_BASELINE=Sgp30Cmd([0x20, 0x15],6,120)
+SET_BASELINE=Sgp30Cmd([0x20, 0x1e],0,10)
 
-def read_write(cmd,bus,addr=DEVICE_ADDR,sleep_time=0):
-    bus.i2c_rdwr(i2c_msg.write(addr,cmd.commands))
-    if cmd.replylen >0 :
-        b=i2c_msg.read(addr,cmd.replylen)
-        sleep(sleep_time)
-        bus.i2c_rdwr(b)
-        r=list(b)
-        crc=r[2::3]
+Sgp30Answer = namedtuple("Sgp30Answer",["data","raw"])
+
+def read_write(cmd,bus,addr=DEVICE_ADDR):
+    write = i2c_msg.write(addr,cmd.commands)
+    if cmd.replylen <= 0 :
+       bus.i2c_rdwr(write)
+    else:
+        read = i2c_msg.read(addr,cmd.replylen)
+        bus.i2c_rdwr(write) 
+        sleep(waittime/1000.0)
+        bus.i2c_rdwr(read)
+        r = list(read)
         answer = [i<<8 | j for i,j in zip(r[0::3],r[1::3])]
         return answer