Integrate External Table Builders into the Main Code

[GoogleCodeExporter]

There are external table builders in the subsetter code that need to be 
integrated into the code for the table they are building. Examples of these are 
HorizontalMetricsTableBuilder and PostScriptTableBuilder. Having these as 
external makes them more difficult to use and to keep up to date with core code 
changes.

Original issue reported on code.google.com by stua...@google.com on 10 Jan 2012 at 1:26