More code cleanups
Introduce PrefPtr typedef
More auto-converts by cpp11-migrate
Cleanup RequestGroup code a bit
Code cleanup in Http*
clang-modernize -add-override on headers
AppleTLS: Remove unused variables
Fix AppleMessageDigestImpl use with large data
WinTLS: Implement messsage digest using the Cryptography Provider
One MessageDigestImpl.h to rule them all.
Only use AppleMessageDigest when using AppleTLS
Add internal md5 and sha1 message digests
Add --disable-ssl configure option
Add some md5 tests