Add MCP23017 (#466)

* Add MCP23017

* Add test

tests/test1.yaml

@@ -613,6 +613,13 @@ binary_sensor:
       number: 1
       mode: INPUT
       inverted: True
+  - platform: gpio
+    name: "MCP binary sensor"
+    pin:
+      mcp23017: mcp23017_hub
+      number: 1
+      mode: INPUT
+      inverted: True
 
 pca9685:
   frequency: 500
@@ -669,6 +676,13 @@ output:
       number: 0
       mode: OUTPUT
       inverted: False
+  - platform: gpio
+    id: id22
+    pin:
+      mcp23017: mcp23017_hub
+      number: 0
+      mode: OUTPUT
+      inverted: False
   - platform: my9231
     id: my_0
     channel: 0
@@ -1140,6 +1154,9 @@ pcf8574:
     address: 0x21
     pcf8575: False
 
+mcp23017:
+  - id: 'mcp23017_hub'
+
 stepper:
 - platform: a4988
   id: my_stepper