Auto-create app dir if we have an appbase.

We were already doing this for bootstrap.properties-based launches, but there's
no reason to restrict it to that. If you run Getdown with an appbase and an
appdir, it can create the app dir and download the app into it.

This enables scenarios where getdown is installed to a shared location and
users that run the app install it in their private storage area (or on a
machine local file system, or who knows).

Closes #163.

CHANGELOG.md

@@ -2,9 +2,14 @@
 
 ## 1.8.1 - Unreleased
 
+* If both an `appbase` and `appdir` are provided via some means (bootstrap properties file, system
+  property, etc.) and the app dir does not yet exist, Getdown will create it.
+
 * Added `max_concurrent_downloads` setting to `getdown.txt`. Controls what you would expect.
   Defaults to two.
 
+* Fixed issue with `appid` not being properly used when specified via command line arg.
+
 * Fixed issue with running Getdown on single CPU systems (or virtual systems). It was attempting to
   create a thread pool of size zero, which failed.