Cache the user configuration from ~/.pplconfig instead of repeated loading

This method was being call dozens of times per execution of ppl. Reading and
parsing that INI file is an expensive series of operations, and this
inefficiency was severely impacting ppl's performance.

I actually measured a speed increase of almost an entire second because of this
change. It's pretty shamefully bad performance in the first place, but at least
this fixes that somewhat. This pretty much fixes h2s/ppl#28, for now at least.

Wow. Sorry everyone, I goofed on this one.