^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

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.

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.

* Add automatic RPM builds via travis

* readline.h must be imported after stdio.h to pick up def of FILE