Created new documentation for GC100 component and platforms (#3789)

* Create gc100.markdown

* Create binary_sensor.gc100.markdown

* Create switch.gc100.markdown

* Fixed formatting of configuration variables

* Elaborated on what gc100 is

* Implemented fabaff's requested changes

removed blank line, updated yaml example to be a list of ports, added period to ports parameter description.

* Implemented changes requested by fabaff

removed blank line, fixed yaml format, added period to ports parameter description

* Fixed ha_release and ha_category

* Fixed ha_release and ha_category

* Implemented changes requested by fabaff.

fixed ha_release and added parameters.

* Updated introduciton description

Implemented suggestion by upsert and referenced iTach library.

source/_components/switch.gc100.markdown

@@ -0,0 +1,31 @@
+---
+layout: page
+title: gc100 Switch
+description: "Instructions on how to set up an gc100 switch within Home Assistant."
+date: 2017-10-27 17:26
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: Switch
+ha_release: 0.57
+ha_iot_class: "Local Polling"
+---
+
+This allows you to control and monitor the relay state on your GC100.
+
+To enable this switch, you first have to set up [gc100](/components/gc100/), and add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+switch:
+  - platform: gc100
+    ports:
+      - '4:1': Siren
+      - '4:2': Sprinkler
+```
+
+Configuration variables:
+
+- **ports** (*Required*): A list of module-address to name mappings in the format 'x:y': name, where x is module #, y is address.
+