=hco,str small cleanups
+hco introduce Uri.Host.inetAddresses for easy access to the actual addresses
=hco more accurate result types for HttpEntity.apply overloads
+hco introduce generic abstract accessor for HttpCredentials parameters
!hco more stringent following of plurally named container object

 - ContentDispositionType => ContentDispositionTypes
 - TransferEncoding => TransferEncodings
 - RangeUnit => RangeUnits
!hco get rid of extra HttpResponse constructor which changes ordering

The problem is that those extra constructors can easily lead to
ambiguities in overloading resolution. We should rely on named parameters
to get a similar effect than those extra constructors.
!hco #15392 use `params` instead of `parameters` consistently
!hco privatize some internal Uri.Host constructors
Merge pull request #15391 from spray/w/small-http-core-changes

+hco Small akka-http-core changes as a preparation for the Java API