Start of init function

The first parts of the init function. This should be the most neccesary
info that the class needs.

sgp30/sgp30.py

@@ -9,7 +9,6 @@ import requests
 import os.path
 
 DEVICE_BUS = 1
-DEVICE_ADDR = 0x58
 BASELINE_FILENAME = os.path.expanduser("~/sgp_config_data.txt")
 
 class _commands():
@@ -31,6 +30,12 @@ class _commands():
 
 class Sgp30():
 
+    def __init__(self,bus,device_address = 0x58):
+        self._bus = bus
+        self._device_addr = device_address
+        self.rw=partial(read_write,bus=bus)
+        self._start_time = time()
+
     Sgp30Answer = namedtuple("Sgp30Answer",["data","raw"])
 
     def read_write(cmd,bus,addr=DEVICE_ADDR):