cpp: Changed mix_states behaviour

Now it don't throw exception but returnes non-positive error_info
object to determine if mix_states was successfull
WIP: Documentation warnings
Added forgotten doc/Doxy*.in files
Get rid of get_node calls
docs: Don't try to install documentation

Debuild/rpm scripts are not ready for it yet
tests: Don't make artifacts if test is successfull
Merge pull request #343 from euroelessar/master

Doxygen & mix_states improvements (master)