In downcase and upcase pattern match tail as ::bits instead of ::binary. This
saves us a check on each iteration if the tail is a proper binary. We only do
this check in the very beginning.
In trim_leading additionally make sure every head of the recursive function
pattern matches on a binary in first argument so the single binary match context
optimisation can be applied.
Ben Olive
José Valim
Michał Muskała
Andrea Leopardi
José Valim