- remove the requirement to use Bintray repo; kotlinx-metadata-jvm is
published to Maven Central now
- remove the note about kotlin.Metadata being internal; it's public
since 1.3
- rename object Flags to Flag and merge it with MetadataFlag
- use typealias Flags instead of Int
- use top level function "flagsOf" instead of "Flags.invoke" to
construct a bitmask
#KT-23198