Make autocomplete value a prop (#730)

What
---
- Turn the autocomplete value on the `input` configurable by exposing it
as a prop.

Why
---
So it can be customised, which can be necessary to help developers show
or hide autocomplete forms as they wish.

docs/gitbook/Api/Props.md

@@ -34,6 +34,16 @@ disabled: {
 	default: false
 },
 
+/**
+ * Value of the 'autocomplete' field of the input
+ * element.
+ * @type {String}
+ */
+autocomplete: {
+  type: String,
+  default: 'off'
+},
+
 /**
  * Sets the max-height property on the dropdown list.
  * @deprecated