Nim 1.6.6 release candidate

[Clonk]

Nim versioning is using even number for release and odd number for devel 
version. This is why the release are 1.0 -> 1.2.0 -> 1.2.2 -> 1.2.4 etc. -> 
1.4.0 -> 1.4.2 -> 1.4.4 etc..

So the release candidate of 1.6.6 is 1.6.5.