^Q would quit even from filter mode

On Mac and error is thrown if the regex expression to regcomp() is empty.

Please refer to comments at:
c42df81ae5

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

Add Debian and Fedora package installation option.

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.

* Bring back plain builds

* Bring back plain builds

* Bring back plain builds

* Bring back plain builds

Limit all xstrlcpy() calls by dest length.
Escape filenames in system(3) calls.

We are converting multi-byte to wide char and vice versa to replace the escape
chars with ?. Otherwise we run the risk of breaking a Unicode code point.