doxygen version 1.8.5 throws many "Internal Inconsistency" errors when parsing .idl files

A number of error messages lacked the '\n' character
Merge pull request #69 from albert-github/feature/idl_err_msg

doxygen version 1.8.5 throws many "Internal Inconsistency" errors when parsing .idl files
usage: make -d print dev doxygen options

This is an extension / improvement to the pull request 67 from  groleo
- make printing of -d levels more flexible (when adding a new one this is now done automatically)
- layout of the message
Merge pull request #70 from albert-github/feature/developer_usage

usage: make -d print dev doxygen options