Functions to implement the number system rule-based-number-format rules of CLDR.

These rules are defined only on the "und" locale and represent specialised number formatting.

The standard public API for RBNF is via the Cldr.Number.to_string/2 function.

The functions on this module are defined at compile time based upon the RBNF rules defined in the Unicode CLDR data repository. Available rules are identified by:

iex> Plausible.Cldr.Rbnf.NumberSystem.rule_sets(:und)
[:zz_default, :tamil, :roman_upper, :roman_lower, :hebrew_item,
 :hebrew, :greek_upper, :greek_lower, :georgian,
 :ethiopic, :cyrillic_lower, :armenian_upper, :armenian_lower]

A rule can then be invoked on an available rule_set. For example

iex> Plausible.Cldr.Rbnf.NumberSystem.roman_upper(123, :und)
"CXXIII"

This particular call is equivalent to the call through the public API of:

iex> Plausible.Cldr.Number.to_string(123, format: :roman)
{:ok, "CXXIII"}