- changes the modules hierarchy to better represent the set of libaries
- list the header file that needs to be included
- remove examples/doc from api ref that is included in the guide
- add references to the guide
- fix doxygen api linking for version 1.8.0
- readd doxygen mainpage to config file
- fix a couple of doxygen doc bugs
The idea of a common handle is long revised and only misleading,
nl_handle really represents a socket with some additional
action handlers assigned to it.
Alias for nl_handle is kept for backwards compatibility.