adds class for crc8 calculations

sgp30/crc.py

@@ -0,0 +1,23 @@
+class Crc8:
+    def __init__(s):
+        s.crc=255
+
+    def hash(s,int_list):
+        for i in int_list:
+            s.addVal(i)
+        return s.crc
+
+    def addVal(s,n):
+        crc = s.crc
+        for bit in range(0,8):
+            if ( n ^ crc ) & 0x80:
+                crc = ( crc << 1 ) ^ 0x31
+            else:
+                crc = ( crc << 1 )
+            n = n << 1
+        s.crc = crc & 0xFF
+        return s.crc
+
+#print(Crc8().hash([1,144]))
+#print(hex(Crc8().hash([0xBE, 0xEF])))
+#[1, 144, 76, 0, 6, 39]