Nim doc issues

[haxscramper]

To-do list for issues specifically related to nim doc output

• [ ] No user-defined grouping for constants, types, procs or any other entries.
• [ ] When non-exported symbol (const set) used as value of object branch selector, documentation does not show the actual value.
• [ ] Arguments that were specified with using declaration don't show final types.
• [ ] Cannot group enums in table/list
• [ ] Related to earlier - documentation comments that are added to object and enum fields are not property processed - just pasted with (bad) formatting in the resulting output. This means any links, references etc. are just plain useless.
• [ ] Almost broken support for --project that requires extensive boilerplate to use, provides pretty pointless results (https://haxscramper.github.io/hmisc/theindex.html - at the time of writing all links to documentable entries were broken with URLs like https://haxscramper.github.io/hmisc/_._/_._/_._/_._/.nimble/pkgs/hmisc-0.12.2/hmisc/algo/htext_algo.html#%24%2CMarkWord)
• [ ] Cannot explicitly provide semantically meaningful documentation for arguments/raises/return-types/side-effects. Doxygen/javadoc have \arg/@arg, and I think these are useful once you get beyond certain complexity in documentation (like documenting callback with default value)