Added photo post with description example

### base64sig.sh works
Works well.  More of a BASH exercise really, but useful not to have to look up the command all the time.

### Facebook SDK 3.5
v3.5 has a bug that has to be fixed manually by the user.  Added to docs.

### FACEBOOK_APP_ID
......whoops.

### Rewrite Underway
My Twitter implementation (uploading soon) doesn't depend on Kivy (except Logger, optional), includes some new code snippets for checking for network connection, toasting, and has a very minimal API for the user.  Since I like it so much, I'm going to make a similar implementation for Facebook and Billing.