Allow to control vimb by fifo file (#144).
Fix segfault on quit by control fifo (#144).

If vimb is closed by the fifo with `echo ":q\r" >> {fifo}` or `echo '<C-Q>' >>
{fifo}`, vimb crashed because of a too early cleanup during allready active
main loop.
The cleanup code is now called right after the main loop is killed.
Don't record commands given by --cmd option.

We don't want to record startup commands in the command history.
Clear inputbox after running command successfully (#104).

If a ex command was run successfully the inputbox is cleared if the command
does not omit this. So the user have a fast response if the command failed or
not. This might be useful for :open command where it could take some time
until the user see if the requested page starts to load or not.
Fixed gcc warning for possible uninitialized variable.
Merge branch 'feature/fifo'.