Fix in documentation to SNESLineSearchShellSetUserFunc()

Arguments in the example code were reversed.  I also styled it better.
Noticed by Sander Land <sander.land@gmail.com>
Clarified docs for SNESLineSearchGet/SetVecs()

Make sure that it's well stated that X and F are solution and function
vectors; W and G are the associated work vectors.
Small formatting fix
Removed the ability of XXXType to be the string name of a library and function in that library but forgot to remove this form from all the XXXAType manual pages