^Q would quit even from filter mode

1. Open directories in filter mode
2. Fix arrow keys not working after filter selection (due to invalid cur entry)
3. Support `Insert` key to clear filter prompt
4. Update documentation

Reasons:

gnome-search-tool is much more powerful than other tools in its category. It
supports numerous search parameters like size, modification date and supports
text search.

This change remaps the & key. However, / is more relevant for filter and & makes more sense wrt. address.

Add .Ed to match with .Bd

It was troubling me. Mimicking 'gg' would have been hacky and would need
additional processing... 'g' was free. Who cares even if you press twice? ;)

We closely follow the output for stat(1).

Original patch written by Richard Hyde and taken from
https://github.com/RichardHyde/noice

Patch written by Richard Hyde and taken from
https://github.com/RichardHyde/noice

Nobody uses it and adds additional complexity.

Fix some mandoc -Tlint warnings as well.