Client and Server 0.15

Fixed

Fix two separate integer overflows from substractions #585 (@oherrala)
strictly enforce name and label lengths during label parsing #584
enforce that only prior labels are used in label expansion, decompression #578 (@oherrala)
CAA now properly performs case-incesitive compares #587 (@oherrala)
overhauled rdata parsers with Restrict type to reduce potential of overflowing operations #586

Added

feature dns-over-rustls to trust-dns-server (server) and trust-dns (client)
feature dns-over-https-rustls experimental #557
new configuration options for tls, see server/tests/named_test_configs/dns_over_tls_rustls_and_openssl.toml
new utility for querying root key-signing-keys, util/get-root-ksks
updated root trust-anchor to include new 20326 RSA root ksk

Changed

Make trust_dns_server::server::ResponseHandler Send #593 (sticnarf)
Wrap types in Restrict and force validation before usage from streams #586
breaking Overhauled all ClientFuture implementations to align with new DnsExchange and DnsMultiplexer components in proto.
breaking ClientFuture after construction, now returns a "background" ClientFuture and a "foreground" BasicClientHandle
breaking Client has more type parameters, these match with the same types returned by the *ClientConnection constructors
breaking all default features, removed: "dns-over-openssl", "dnssec-openssl". Use --features=dns-over-openssl,dnssec-openssl to enable
breaking named configuration now has AXFR disabled by default.
breaking Migrated from error_chain to Failure #474 (@silwol)
feature tls renamed to dns-over-openssl
upgraded native-tls and tokio-tls to 0.2
upgraded rusqlite to 0.15