Do not reset selection on search when 'nohls'

Thanks to filterfalse.
Extract print_result() function from find_pattern
Add heading comment for search:find_pattern()
Remove useless move parameter of find_npattern()
Fix a typo in vim-help on vifm-n command
Fix displaying of search results message

This time for different combinations of 'wrapscan' and 'hlsearch'
options states.  Now all (I hope) should work as expected, because the
main issue was found (wrong treating of find_pattern() result, as match
signal instead of message signal).
Extend documentation of n/N keys a bit

Note conditions under which selection is reset.
Merge branch 'do-not-reset-selection-on-search-and-nohls'
Fix ack/ag arguments in examples of documentation

Thanks to filterfalse.
Universalize :invert command

Make it accept an argument that specifies one of three (at the moment)
features that can be inverted:
 - "f" - filename filter
 - "s" - selection in current view
 - "o" - primary key of sorting

Both :invert and :invert? forms of the command were extended to support
an argument.
Preserve current cursor position on view resort
Provide :invert[?] completion
Extract function for list-based completion
Don't let completion of eat all available memory

Related to :history and :invert.  Used to be possible by pressing
<tab> key multiple times.
Update documentation about the :invert command
Fix video file preview command in sample vifmrc

Thanks to filterfalse.
Provide proper highlighting of :invert command
Fix highlighting of comments after :let statements

Thanks to filterfalse.
Merge branch 'enhance-invert-command'