- remove support for LIBT2N_EXPORT_GROUP(group) (this will simplify the generator a lot)
- add option similar to gccs -MD (at the moment it is a fixed set of files generated and
  they are handled in the makefile)

open questions:
- should projects using the codegen depend on installed version of ... or ship their own version?
	* codegen binary: no
	* Makefile snippet: no
	* codegen-stubhead.hxx
- get rid of codegen-stubhead.hxx or include a "copy" in each project
- makefile snippet must work for builds outside of libt2n
  (=> some variables must be set by configure, the snippet must be installed
   => pc file template must be installed, too)
- it would really be much nicer if the client lib includes would not depend upon boost serialization
  i thought a solution would be to provide this optionally by wrapping the corresponding includes in a #ifdef
  but this does not work since command.hxx is included which depends on boost serialization headers anyway
  => we do not provide this for now