Add support for using plaintext code output when pygments is not present, rather than failing entirely.
Add support for using plaintext code output when pygments is not present, rather than failing entirely.

tbremer/docco,oponder/docco,jalleyne/docco,whitetrefoil/docco,jrvidal/docco,ShawnHuang/docco-multidir,Hellyna/docco,tbremer/docco,lbn/docco,mhkeller/docco,guigrpa/docco,jrvidal/docco,erikdiessel/plidoc,osharim/docco,ShawnHuang/docco-multidir,MaxwellRebo/docco,STRd6/docco,guigrpa/docco-extended,erikdiessel/plidoc,DoomHammer/docco,osharim/docco,JonathanMatthey/codeconv,Hellyna/docco,oponder/docco,DoomHammer/docco,lobrien/docco,robertmackenzie/docco,actano/docco,MaxwellRebo/docco,gvithellyna/docco,jalleyne/docco,lobrien/docco,robertmackenzie/docco,mhkeller/docco,gvithellyna/docco,whitetrefoil/docco,guigrpa/docco-extended,guigrpa/docco,HubSpot/docco,lbn/docco