Merge branch 'build'
Add missing <stdexcept> include
Fix linking issues
Add types::Dict typedef
Add `at` function to Index_node
Re-add get_descendant functions to Index_node
Merge branch 'fixes'
Revert events::Broadcaster to non-blocking
Add events::Forwarder Interface
Add events::Blocking_forwarder
Add events::Detaching_forwarder