Integrate new 2.13 collection types

[lrytz]

Provide (optimized) stream converters (if necessary?) for new collections in 2.13

• ChampHashSet / ChampHashMap (they will probably be renamed to HashMap / HashSet)
• mutable / immutable ArraySeq
• ArrayDeque

[SethTisue]

for now on the 2.13.x branch I removed the references to the old HashMap, to get the 2.13 community build green: 3334e28

[SethTisue]

@lrytz should this be closed?

[lrytz]

Yep, at least here :-)