base::config()

Documentation example for custom configuration sections (http://fatfreeframework.com/framework-variables#Customsections) was not working for me.
- regex for lval wouldn't match variables that are single letter
- variables in custom sections were not being prefixed with the section name - just added directly into globals

This alters the regex to allow single-character variables, and adds the section prefix when the section is not 'globals'.  Now the `[foo]` ... `[foo.hash]` example works.

Question: is this the correct way to add the section prefix?