Mentions of the new database update runtime mode and update of
the legit module and the dummy part too.
Note the DeviceAtlas C API version 2.4.0 minimum required
alongside with libCURL, libzip and libgz.
Both the source file and the dummy library are now at the same place.
Maybe the build howto could be moved there as well to make things even
cleaner.
The Makefile, MAINTAINERS, doc, github build matrix, coverity checks
and travis CI's build were updated.