Minor `transcoding()` doc improvement.

Moved the note about the contract to the Params: section, which until now was pretty useless.

A user checking the function's parameters  will usually look at `Params:` first and may miss any text about e.g. requirements of a parameter if it's not mentioned there in `Params:`.
Minor doc bugfix and changes of subscript definition
Merge pull request #2819 from kiith-sa/patch-3

*trivial* `DDoc` Minor `transcode()` doc improvement.
Merge pull request #2823 from andralex/doc

Minor doc bugfix and changes of subscript definition
remove stray paren
Merge pull request #2824 from andralex/doc

remove stray paren
Group encode overloads together again
Fix docs for encode overload
Merge pull request #2825 from ntrel/encode-docs

Fix docs for encode overload