Print version of libraries and features

[rodarima]

When reporting the version of Dillo with -v, print also the version of
the libraries it is currently using, as well as the features that were
enabled at build time. Notice the versions are reported by reading them
at runtime, so we can detect the version loaded at run time, regardless
of which version was used at link time.

All features are always printed, but prefixes with + if enabled or - if
disabled. This allows checking if the feature was disabled at configure
time or if it is missing in that version of Dillo.