Add option to indent output in encoding/text

[martin-sucha]

Indented output is more readable.

[zombiezen]

Thanks for the PR! Here's some areas that I think can improve before we merge in:

[zombiezen]

I wonder whether the calling logic becomes simpler if NewLine and NewLineOrSpace were removed and the indentWriter would automatically apply this logic when a \n is encountered in its stream. WDYT?

[martin-sucha]

I think it would complicate the code instead of simplifying it. indentWriter would need to parse all the strings for \n, so the write couldn't just pass the buffer to the underlying writer. On top of that, we have NewLine which inserts a new line or nothing and NewLineOrSpace which inserts a new line or space. We need to distinguish those two cases, which would mean that we'd need to mark it somehow in the stream, complicating the parsing logic further. So I'd rather keep NewLine and NewLineOrSpace as they are now.

[zombiezen]

Acknowledged.