Modularizarion by npm and all-in-one bundle by browserify

Split and modularize power-assert-formatter.js internals

- [x] Build all-in-one bundle by browserify
- [x] Migrate to gulp
- [x] Modularize
- [x] Extract [type-name](https://github.com/twada/type-name) module
- [x] Dealing with east asian width
- [x] Surrogate pair?
- [x] Separate context traversal from renderling
- [x] Splitting various renderers