ESM Support

[codekrafter]

Right now when using pbf in an angular application (or using a library that depends on pbf), angular emits a warning about using commonjs/amd dependencies, as they cause optimization bailouts and interfere with tree shaking.

Providing an esm module would fix these warnings and allow better optimization.

[measuredweighed]

A little late to the party, but I ended up creating a fork to generate esm modules which should act as a drop-in replacement for existing implementations in the short term.