Space after in, out and invariant

[belka-ew]

According to the D Style there should be a space after in, out and invariant in contracts.

< in (value % 7 == 0)
< out (result; result % 11 == 0)
---
> in(value % 7 == 0)
> out(result; result % 11 == 0)

[WebFreak001]

this should probably be controlled by dfmt_space_after_keywords (default true) which still needs to be implemented, but seems to currently be an inconsistent default