bash: prompt improvements
bash: prompt improvements

Port over @alrra's improvements to prompt performance and code
organization.

jmyser/dotfiles,bronxct1/dotfiles,bronxct1/dotfiles,lgaechter/dotfiles,sdillingham/dotfiles,necolas/dotfiles,codfish/dotfiles,pmacom/dotfiles,SBoudrias/dotfiles,pertoyra/dotfiles,SiTaggart/dotfiles,seiryu9/dotfiles,codfish/dotfiles,saclark/dotfiles,seiryu9/dotfiles,marc0uk/dotfiles