Merge pull request #1 from pydave/master

Support search history
catch error if pattern is not found
add a feature: grep current directory with searched word
Display error when pattern is not found

When a plugin does an action (like n) that results in an error (not
found), vim raises an exception (so you see stack trace information).
That's not useful. But we do want to see the error, so emulate the
interactive mode error (output the message in error text).