load images and fonts from executing dir

[akinsho]

Fixes #141 @bryphe hopefully this addresses the problem of loading fonts and images using esy x Bin (tested and does work) in the way you intended

[jchavarri]

This is awesome @Akin909 ! 🎉 Some related thoughts:

• The esy.json file I think it's an artifact used by older versions of esy. In the most recent versions, it was replaced by an esy.lock folder
• The addition of Sys.getcwd() probably will have some implications in projects targeting the browser through jsoo. js_of_ocaml doesn't support Sys that much, and from a quick test I did, it returns /static which doesn't make any sense in the folder structure of the test project I was using (there is no folder in that project called static). So maybe we have to create some abstraction over the different platform implementations like happened with fontkit or glsw. Maybe we could call it reason-system... or build it from rench (although, rench is more opinionated towards a Node.js-like API as far as I understand). I'd be happy to look into this as part of Fontkit.js support #116.
• Probably out of scope 😄 but I'd love to play around ideas around handling compile-time known assets paths at build time. I'm still unsure how that would look like exactly, but my idea right now is to read these paths at compile time, maybe through a ppx, read the assets from the ppx binary, and convert the load expression into an assignment to a binding of the whole path binary data (maybe as a string? or as binary data?). Something like https://github.com/johnwhitington/ppx_blob.

[OhadRau]

Awesome work so far! This is a great first step towards shippable revery software.

@jchavarri If you're interested in compile time asset loading, that's some thing I was gonna try to make actually. I've thought of a few ways of doing it and once I settle on one I'll go ahead and write a PPX for it:

• Automatically guessing which files are statically accessible (if the path given to whatever File.load is a string literal && the file exists)
• Having a [@static] annotation that can be used when loading a file to inform the compiler that it's a static asset
• We can output each file as a linkable object file (e.g. https://www.linuxjournal.com/content/embedding-file-executable-aka-hello-world-version-5967) and generate extern declarations
• We could also make an array or hashtable of strings (binary or otherwise) that we load, basically the same as what ppx_blob would do
• For each of these, we have to let File.load know that these files are already loaded. We can do this by using a hashtable/other data structure of cached files and then inserting that as an optional parameter/overriding an empty data structure when we've loaded files

[akinsho]

@jchavarri good point re. Sys not working in all environments 👍, you sound like you've given it way more thought than I did so for this PR I've just put a guard to only try the Sys call if the env is native, but an actual future solution that can do a similar thing per environment would be awesome.

Re. the esy.lock.json, it seems to have already been in the project, is it unnecessary now, seems to change whenever I run esy on a branch without necessarily changing dependencies.

The ppx idea sounds very cool (I'm new to reason and ocaml so would be beyond me at this point 😆 )

[bryphe]

Just tried out this PR - I can now run esy x Bin.exe on Windows! 🎉 This makes it so much easier to run the demos (at least for me), and means #136 is unblocked now. Thanks @Akin909 for the change, and @jchavarri and @OhadRau for reviewing!

@jchavarri @OhadRau - that is a really cool idea for the compile-time asset loading! 😍 I don't want to lose the context of the discussion once this goes in, so I ported some of the thread over to #157