* identity.scm: `open-identity-service` now throws an exception on failure.
* binding-utils.scm: just add `destructuring-bind`.
* common.scm: `time-rel` now throws an exception instead of returning a
meaningless negative result; add `setup-log`.
* container/metadata.scm: `metadata-set!` now throws an exception on error.
* tests/container-metadata.scm: add tests for `metadata-copy`,
`metadata-clear`, `metadata-equal?`
and `add-publication-date!`
* examples/search-ns.scm: a basic tool to search namespaces.
* examples/identity.scm: a basic tool to list egos.
* examples/identity-bis.scm: idem, but using `start-identity-lookup`.
* fs/uri.scm: `wrap-uri` throws an `invalid-arg` exception when given a
null pointer.
* tests/uri.scm: c.f. ↑
* configuration.scm: add `configuration-value-set?`.
* identity.scm: add `ecdsa-public-key->string`.
* common.scm: add `gnunet-id-ffi` (FFI for libgnunetidentity).
* identity.scm: replace `define-gnunet-fs` with `define-gnunet-id`.
* fs.scm: corrects a bug in `start-publish` (gave `GNUNET_FS_publish_start` a
pointer to the ego in place of a pointer to its private key).
* examples/publish.scm: add handling of namespaces and replace simple global
variables with parameters.
* identity.scm: complete bindings of GNUNET_FS_IDENTITY
* fs.scm: add support for egos/namespaces to `start-publish`
* binding-utils: remove the useless import of `assert`