Slightly updated plugin related documentation

Added a note about how to pick files after vifm is spawned.

Thanks to Stéphane (a.k.a. istib).
Merge branch 'update-plugin-docs'
Always set number of matches after search
Extract is_{for,back}ward_search() in cmdline.c
Show message when incsearch & nothing was found
Add print_search_msg() function to search.c
Show message when incsearch & something was found
Note fix of search messages in the ChangeLog
Fix behaviour on 'incsearch' and 'hlsearch'

For the case where something was found a message stating number of
selected files should be printed.
Merge branch 'fix-search-msg-and-incsearch'
Log incorrect usage of the path_exists() of fs.c

When relative path is passed.
Note path_exists() constraints in function comment
Don't check "." for existence in split_path_list
Correct syntax of parameter list of path_exists()
Specify directory for check_file_rename()
Document fixing of the rename issue in ChangeLog
Merge branch 'fix-rename-newname-check'