Various doc improvements for graph adaptors (#67)

- Add notes about modifying the adapted graphs through adaptors
if it is possible.
- Add notes about the possible conversions between the Node, Arc and
Edge types of the adapted graphs and the adaptors.
- Hide the default values for template parameters (describe them
in the doc instead).
- More precise docs for template parameters.
- More precise docs for member functions.
- Add docs for important public typedefs.
- Unify the docs of the adaptors.
- Add \relates commands for the creator functions.
- Fixes and improvements the module documentation.

 EXTRA_DIST += \

 	demo/CMakeLists.txt \

 	demo/digraph.lgf

 if WANT_DEMO

 noinst_PROGRAMS += \

 	demo/arg_parser_demo \

 	demo/graph_to_eps_demo \

 	demo/lgf_demo

 endif WANT_DEMO

 demo_arg_parser_demo_SOURCES = demo/arg_parser_demo.cc

 demo_graph_to_eps_demo_SOURCES = demo/graph_to_eps_demo.cc

 demo_lgf_demo_SOURCES = demo/lgf_demo.cc