Replace Handlebars singularize/pluralize helpers

Replace the handlebars singularize/pluralize helpers with a single pluralise helper that takes two arguments, the count and the word.

I'm not sure the removal is acceptable as it's removing functionality from a released version, but welcome feedback.
TBH, I don't think it's as readable, I can almost guarantee I'd get the argument order wrong every time.
How horrible of an API idea would it be to support `{{pluralize <optional count> word}}`?