Applied the changes which somehow vanished during my last merge. Thanks goes
to Marci for noticing this. In detail:
- added amsmath and amssymb latex packages for latex documentation
- src/demo is also scanned for doxygen input files
2 g++ -ggdb --no-inline graph-displayer.cc -W -Wall -ansi -pedantic -o gd `pkg-config libgnomecanvasmm-2.6 --cflags --libs` -I../..
5 g++ xy-reader.cc -W -Wall -ansi -pedantic -o xyr -I../..