Doc improvements for Bfs, Dfs, Dijkstra (#185)

- More precise references to overloaded member functions.
- Hide the doc of the traits class parameters.
- Better doc for named groups.
- More precise doc for the case of multiple sources in Dfs.

if WANT_TOOLS

bin_PROGRAMS += \

	tools/dimacs-to-lgf

dist_bin_SCRIPTS += tools/lemon-0.x-to-1.x.sh

endif WANT_TOOLS

tools_dimacs_to_lgf_SOURCES = tools/dimacs-to-lgf.cc