Extensions

- Created scripts/extensions/README to describe samples.
- Created sample extension scripts of each type.

scripts/add-ons/README

@@ -0,0 +1,16 @@
+External Scripts
+----------------
+
+Add-on scripts are executed vi an alias mechanism in taskwarrior.  This has the
+effect of this command:
+
+    task <script> <arguments>
+
+resulting in the ultimate execution of:
+
+    <script> <arguments>
+
+All external scripts are treated in the same manner, and have no access to the
+taskwarrior internals.
+
+---