Ignore errors when getting the list of Ansible modules

Ignore the standard error of the subprocess, and parse the output with
buffer commands instead of process-lines
Improve prompt for ansible doc

If the symbol at point is no ansible module, don't suggest it as
default.  Also require a match.
Replace custom functions with ansible-doc package
Remove RefTeX optimizations

My systems are fast enough
Don't save Magit Mode buffers in Desktop