Before this change all targets were displayed in the top level directory of
the project. Now the targets are displayed in the correct directory.
The targets "clean" and "all" are now created in every subdirectory.
Also now the targets for just compiling one file, preprocessing one file,
assembling one file are are created for Eclipse.
Additionally all targets get a prefix now in eclipse, so that they are
sorted in a way which makes sense (global targets first, then executable and
libraries, then object files, then preprocessed, then assembly). Also
this prefix gives the user a hint what the target is, i.e. whether it's a
library or an executable or something else.

Alex