Rewrite interface (v3.0)

[borgar]

Dramatic overhaul of the parser and interface inspired by #42, the need to expose types (#38), and locale issues (#23).

Changes from 2.0:

• Formatters are no longer constructed. Formatting is just a simple call.
  Fixes: Is there any real need for the "create a formatter" mechanism? #42

• Types are now exposed for the entire interface.
  Closes Add "numfmt.d.ts" to package.json as types entry #38

• nbsp option is now off by default. A non-breaking space is till used as the grouping separator in the default locale, so "13 203" should not linebreak.

• formatColor() now returns null if pattern does not define a color. Previously it would default to "black".
  Fixes Consider indicating whether "black" color is explicitly specified or assigned as a default #40

• locale has been fixed so that a pattern may correctly override a locale. The expected behaviour is to be able to provide a default locale and that formatters override it by modifiers.

• Both en_US and en-US styles are now supported for locale tags.

• Group sizing is now controlled by an option, { grouping: [ 3, 3 ] }
  The formatter had remnants of behaviour from its ancestor which allowed defining group sizing in the format. In Excel, #,##,##0 and #,##0 are equivalent but sizing is controlled via locale settings.
  Fixes Comma operator does not work correctly #48

• dateToSerial() no longer passes non-dates through. If it gets incompatible input (such as a number), a null will be returned.

• nativeDate option has been removed. This affects two things:

  • dateFromSerial() now always returns a date parts array ([ y, m, d, ... ]).
  • parseValue()/parseDate() can no longer return dates.

  If you need the old behaviour then here is a utility function that safely converts the output to a Date.

  function toNativeDate (dateArrray) {
    const [ y, m, d, hh, mm, ss ] = dateArrray;
    const dt = new Date(0);
    dt.setUTCFullYear(y, m - 1, d);
    dt.setUTCHours(hh, mm, ss);
    return dt;
  }