Refactor

[z-------------]

• Supports encoding/decoding directly from/to objects, including the old BencodeObj and std/json's JsonNode, via JSONy-style parse hooks and dump hooks.
• Supports decoding at compile-time.
• Supports -d:nimPreviewSlimSystem and plays nice with --experimental:strictDefs.
• Should be mostly backwards-compatible, except:
  • The toBencode macro has been renamed to toBencodeObj (toBencode is now used for encoding objects to bencode).
  • The json submodule is no longer imported by default. Explicitly import it with import pkg/bencode/json and consider using the new fromBencode/toBencode interface instead.