Provide regexes to `bulkReplace` when possible

[pillowfication]

The bulk-replace package creates a new RegExp every time if one is not provided. Providing a regex offers a significant performance boost.

// Initial transliteration
// str = bulkReplace(str, /[ｦ-ﾝ][ﾞﾟ]/g, katakanaHalfwidthsCombined);
// str = bulkReplace(str, /[ｦ-ﾝ]/g, katakanaHalfwidths);
str = bulkReplace(str, /[ぁ-ゖゟ][ぁぃぅぇぉゃゅょ]/g, hiraganaDigraphs);
str = bulkReplace(str, /[ァ-ヺー][ァィゥェォャュョ]/g, katakanaDigraphs);
str = bulkReplace(str, /[ぁ-ゖゟ]/g, hiraganaMonographs);
str = bulkReplace(str, /[ァ-ヺー]/g, katakanaMonographs);

JSPerf: https://jsperf.com/katakana-monographs

[lovell]

Happy to accept a PR if you're able.

[lovell]

v1.2.1