rename/alias and then obsolete UDPSocket::send
The method name "send" on UDPSocket https://ruby-doc.org/stdlib-2.5.0/libdoc/socket/rdoc/UDPSocket.html#method-i-send is confusing and inconsistent.
The underlying libc method is called sendto(2) (or sendmsg()). The method "send" is confused with https://ruby-doc.org/core-2.5.0/Object.html#method-i-send
1. we rename it to sendto, leaving an alias.
2. mark UDPSocket::send as obsoleted
3. remove it in a future version
Some things like Celluloid::IO and the like will need encouragement to duck type the new interface sooner.