horst: update to version 4.1

4.1 has an important bugfix for platforms (such as ARM cns3xxx) where "char"
does not default to "signed char" and other bugfixes.

Also build with debugging enabled (-D flag) to enable debugging, the size
increase is just +336B (on platform au1000).
Merge pull request #363 from br101/master

horst: update to version 4.1