Add documentation to hxd.fs package

[Yanrishatum]

What the title says. Added documentation to hxd.fs package files.
It'll sit as a draft for a week or so, in case someone would want to fix my grammar or point at other issues.

Extra: Fixed some typos in private function methods of FileConverter

As usual, current up-to-date documentation available here: https://wb.yanrishatum.ru/heaps/api/
Coverage report: https://wb.yanrishatum.ru/heaps/api/coverage.html

[ncannasse]

I don't think we should document implementation details here, like "Does nothing initially" or "should be overidden".
Basically all these are implementation from FileSystem so we should refer as the interface documentation instead, and introduce only the class in class header.

Note also that BytesFileSystem is not meant to be actually used by user, it's only here as a dummy implementation for hxd.res.Any.fromBytes

-- Same remark for BytesFileEntry

[Yanrishatum]

I don't really agree on that. If implementation have specific behaviors or plain up requires user to override the method to utilize the class - it should be noted in the documentation.

I actually always perceived it as a jumpstart to implement your own FS without going too deep into the custom FS specifics, and I do thing it has such an utility, which is portrayed in the docs.

[ncannasse]

I would agree in general, but BytesFileSystem is very specific and not really meant to be extended. The good way to implement a FS is to implement the FileSystem interface, that should be the one recommanded.

[Yanrishatum]

Altered the documentation to explicitly state it's intended for internal use and point at Any.fromBytes, but I've kept the mention of alternative use-case for it.

[ncannasse]

I don't think we should specify implementation details in source documentation (such as which exe is called and parameters). Maybe we should have instead all these converts refer to online wiki page where we list them and eventually add some details with links to download the software etc.

[ncannasse]

So I think for all default converts I prefer a single class documentation:

/**
   One of the defaults resource converters available, see [link-to-convert-doc] for more details.
**/

[ncannasse]

Same here, these should only be documented in FileSystem, no duplicate documentation here.

[ncannasse]

FYI I have submit a request to documentation generation tool regarding this
HaxeFoundation/dox#280

[ncannasse]

Thanks ! I did a full review :)