code generator using gccxml and libxml++

for example usage take a look at the libt2n-example package

design decisions:

installation of codegen-stubhead.hxx:
codegen-stubhead.hxx is installed because the generated includes depend on the libt2n headers anyway

make file snippet moved into libt2n-example1 and must be copied manually:
automake is run first (before configure) and needs the makefile snippet => no way to let configure
find the makefile snippet

examples in separate packages:
- this was done to be able to test that installation and configure scripts work as intended
- there are two examples because one is used to generate the usage example documentation using doxygen
  and one is used for automatic testing
- in libt2n-examples there is a script test-built-install-use to test everything is fine

group header file for include file dependencies:
- simple
- i don't see a solution using gccxml
- better than extracting all the includes from the file and adding them to the generated code
