Update and test PSDraw

 * Update PSDraw to work with Python 3.
 * Add a sanity test case. Previously it was completely untested and not shown in the coverage, not even as 0%.
 * Tested locally with Python 2.7 and 3.4 and a valid .ps file is created with the tests. 
 * The PIL handbook gave example code showing a `textsize()` function, which apparently was never implemented. Removed, and from docs.
 * `setink()` just printed out print("*** NOT YET IMPLEMENTED ***") and has been unimplemented since at least PIL 1.1.1 from 2000. Fourteen years is long enough, I've removed it.
 * Fixes #1046.
 * Helps a bit towards #722: PSDraw.py is now 84.38% covered.