chore: Fix title underline lengths in fluent.runtime/CHANGELOG.rst

fluent.syntax 0.19.0 fluent.runtime 0.4.0

fluent.syntax 0.18.1

fluent.pygments 1.0 fluent.syntax 0.18.0 fluent.runtime 0.3.1

fluent.pygments 1.0 fluent.syntax 0.18.0 fluent.runtime 0.3.1

fluent.pygments 1.0 fluent.syntax 0.18.0 fluent.runtime 0.3.1

fluent.runtime 0.3.0

fluent.syntax 0.17.0

fluent.runtime 0.2

Pick up fluent.syntax 0.17 as requirement, and release something
with Fluent 1.0 Syntax.

Also more dependency updates.

Initial commit of a pygments plugin for Fluent formatting.