doc: README: Document avrtest_ulpf.
add: host.c: Implement double emulation on big-endian hosts.
add: host.c: Implement float emulation on big-endian hosts.
fix: run-avrtest-sh: Use bash to run it.
leave: Own exit stati for no IEEE single / double emulation.
fix: avrtest.h: Silence pedantic warning for __[u]int24.
fix: avrtest.h: Remove ; outside of functions.
fix: Makefile (HasMcu): Fix order of redirections.
fix: Makefile: Only compiler a target .o when -mmcu is supported.
doc: README: Typo.
