This was becoming heavy to manage.

This is the first commit I do entirely in VE. It's a habit I'm planning
on taking as it helps a lot to find usability issues.

Make F search from curpos+1 so that it's possible to search the
same word we've just found a second time. Previously, it would find
the word under the cursor.

Also, improve docs a bit.

Previously, it would keep the old buffer displayed why typing over
it. I had kept it thus because I didn't want to erase the buffer
right away because the behavior is that when we type nothing, we
keep the buffer as-is and repeat the action.

Now, the behavior of I and F is much better. It keeps the buffer
displayed until the first non-return keystroke and then erases it.

Also, fixed PSP leak in _type and fixed PSP overuse in successful
_F (they balanced out).