Support for AMD and corrected browser

[harryxue1999]

• Added load support for AMD (such as requirejs)
• Added load support for CMD (as well as NodeJS)
• Corrected browser implementation (script not loaded by script tag may not have arc defined in window)

[jgravois]

hey @harryxue1999!

thank you for taking the time to propose this change and sorry for the belated response! turning arc.js into a UMD is still definitely an option but at this point it has also become pretty common for library authors to publish a bare ES module and let the consumer handle transpilation.

i'll need to chew on this a bit but i'm interested in more feedback if you (or anyone else) has opinions on the topic.

(maybe something like this? https://github.com/felixge/node-dateformat/pull/183)

[jgravois]

a few more years have passed and i'm more convinced than ever that a native ESM rewrite would be the way to go. i don't have any plans to tackle anything like that myself, but a PR would definitely be welcome. 🙏