function GlyphSet(font, glyphs) {
    this.font = font;
    this.glyphs = {};
    if (Array.isArray(glyphs)) {
        for (var i = 0; i < glyphs.length; i++) {
            this.glyphs[i] = glyphs[i];
        }
    }

    this.length = (glyphs && glyphs.length) || 0;
}
A GlyphSet represents all glyphs available in the font, but modelled using
a deferred glyph loader, for retrieving glyphs only once they are absolutely
necessary, to keep the memory footprint down.
@exports opentype.GlyphSet
@class
@param {opentype.Font}
@param {Array}