Added replace mode extension
Added paste and replace mode colourings to themes
fix regression with modified state being lost when switching windows.
shorten inactive windows to only the filename. resolves #35. also, treat inactive as a mode so it can be themed independently.
add netrw support. resolves #31.
refactor colors to use color map generator
support undotree, gundo, nerdtree, tagbar
use list of funcrecs, allowing window overrides to be dynamically added