Make it work on Windows

[calebeby]

Hello and welcome to my pull request. The following are things about Windows that make me sad.

• ☹️ Windows paths start with C:\ (or similar). On Windows, we need to handle those as absolute paths.
• ☹️ Windows paths (usually) have \ instead of /. On Windows, we need to use \ for any path used on the file system, and / for any path used in the browser. In a lot of cases Windows doesn't seem to care which one you use, but I don't know if that is universally true (and if you ask for a path it will always give you one with \ AFAICT)
• ☹️ Windows files have \r\n (CRLF) instead of \n between each line. This is not always true though; for example git for windows can be configured to checkout files as-is from GitHub instead of converting them while performing a checkout. So they can have either \r\n or \n. But text files in the browser (e.g. HTML, CSS, JS) will have \n instead since they are not on the filesystem. So we need to handle both.
• ☹️ The fact that windows paths usually use \ which happens to be the escape character for JS strings makes things more difficult, e.g. you can't plop a windows path into a JS string with ${} directly because of the escaping. Don't ask how long I spent debugging a string that once interpolated became something\node_modules and the \n in the middle was seen as a line break so then I was like "what is ode modules I do not like it" 😱 🙀 😡
• ☹️ Windows paths are case insensitive so they must be normalized before they can be compared

[Paul-Hebert]

Thanks Caleb! Code looks good and tests are passing 👍

I left a few small non-blocking suggestions that you may want to take a look at before merging. Thanks!