Add toast component documentation

- Add documentation that describes when and how to use a toast message
with code snippets
- Add an informational toast method in the BVToastMixin
- Add BVToastMixin to enhaceApp to register mixin globally.

Signed-off-by: Derick Montague <derick.montague@ibm.com>
Change-Id: I89bf2aa8b3fdb9294354a80c98ccf692b6e3615a
diff --git a/docs/.vuepress/config.js b/docs/.vuepress/config.js
index 2be074e..680c98e 100644
--- a/docs/.vuepress/config.js
+++ b/docs/.vuepress/config.js
@@ -45,6 +45,7 @@
             children: [
             "/guide/components/",
             "/guide/components/button",
+            "/guide/components/toast",
           ]
           }
         ],