Number Format (format and parse)

Formatter types: URBNF_SPELLOUT, which creates a formatter that spells out a value in words in the desired language, URBNF_ORDINAL, which attaches an ordinal suffix from the desired language to the end of a number (e.g. "123rd"), URBNF_DURATION, which formats a duration in seconds as hours, minutes, and seconds, and URBNF_NUMBERING_SYSTEM, which is used to invoke rules for alternate numbering systems such as the Hebrew numbering system, or for Roman Numerals, etc.

```
icu::RuleBasedNumberFormat::RuleBasedNumberFormat ( URBNFRuleSetTag tag,
const Locale & locale,
UErrorCode & status
)
```

```
virtual UnicodeString & format (double number, UnicodeString &toAppendTo, FieldPosition &pos) const
```

parse: lenient...