Parsing speedups

I've been profiling the core installman script, which turns out to be mostly Pod-Simple and Pod-Man. For starters, here are a few quick optimisations that don't impact readability much. The changes reduce the time spent in Pod::Simple by 15-20% and the overall runtime of installman by about 5%

https://rt.perl.org/rt3/Public/Bug/Display.html?id=116485