Renamed the `Backend`'s `compilerAnnotation` field to `nativeAnnotation` and removed the now unneeded `doc` backend (ceylon/ceylon-spec#500)
Renamed the `Backend`'s `compilerAnnotation` field to `nativeAnnotation` and removed the now unneeded `doc` backend (ceylon/ceylon-spec#500)

jvasileff/ceylon-common,ceylon/ceylon-common,ceylon/ceylon-common,ceylon/ceylon-common,jvasileff/ceylon-common,jvasileff/ceylon-common