[BUGFIX] Fix support for multi-part namespace identifiers
This change fixes support for namespaces containing dots.
Previously the ``TemplateParser`` skipped those when used in "shorthand
syntax" and something like::
was never replaced.
This limitation is not new but it was easy to work around in previous
versions. Since Flow package keys are registered as namespace
identifiers (see FLOW-151) this issue became more urgent.
Releases: master, 3.0