Fix missing reprogrammable keys

The assumption that the Features IDs are in increasing order does not
hold. This causes the feature check for REPROG CONTROLS (1B00) to fail,
therefore remove the micro-optimisation.

While at it, rename variables and document the functions better.

lib/logitech_receiver/hidpp20.py

@@ -210,9 +210,10 @@ class FeaturesArray(object):
 				indices = index.indices(len(self.features))
 				return [self.__getitem__(i) for i in range(*indices)]
 
-	def __contains__(self, value):
+	def __contains__(self, featureId):
+		"""Tests whether the list contains given Feature ID"""
 		if self._check():
-			ivalue = int(value)
+			ivalue = int(featureId)
 
 			may_have = False
 			for f in self.features:
@@ -220,8 +221,6 @@ class FeaturesArray(object):
 					may_have = True
 				elif ivalue == int(f):
 					return True
-				elif ivalue < int(f):
-					break
 
 			if may_have:
 				reply = self.device.request(0x0000, _pack('!H', ivalue))
@@ -231,17 +230,16 @@ class FeaturesArray(object):
 						self.features[index] = FEATURE[ivalue]
 						return True
 
-	def index(self, value):
+	def index(self, featureId):
+		"""Gets the Feature Index for a given Feature ID"""
 		if self._check():
 			may_have = False
-			ivalue = int(value)
+			ivalue = int(featureId)
 			for index, f in enumerate(self.features):
 				if f is None:
 					may_have = True
 				elif ivalue == int(f):
 					return index
-				elif ivalue < int(f):
-					raise ValueError("%r not in list" % value)
 
 			if may_have:
 				reply = self.device.request(0x0000, _pack('!H', ivalue))
@@ -250,7 +248,7 @@ class FeaturesArray(object):
 					self.features[index] = FEATURE[ivalue]
 					return index
 
-		raise ValueError("%r not in list" % value)
+		raise ValueError("%r not in list" % featureId)
 
 	def __iter__(self):
 		if self._check():