init mutex after
check arguments number using argc and optind
improve usage display
implement push function

Pushing 'p' now opens the file in your
editor and when quitting it later,
the search results are still present.

Pushing Enter has the old behaviour.
Merge branch 'master' of git://github.com/jonathanklee/ngp

Conflicts:
	ngp.c
Apply rolling wheel change of style patch