require formatter registration
extract formatter management
Formatters support supplying information about notifications
html formatter doesnt need to extend base text formatter
handle legacy formatters
Documentation and cleanup
remove `Formatters::Collection#clear`, it's not needed.
refactor formatter collection to loader
restore early deprecation warnings
yard for legacy
reporter handles (ignores) duplicated listener notifications
ignore string vs symbol notifications and treat identically
remove to_a
fixup specs (to be refactored more)
check legacy formatter by behaviour
refactor specs to use formatter support (sends via reporter)