Add newlines after too many deprecations warnings

Created by: soulcutter

This is for #1147 (closed)

I liked your heredoc pipe trick from a recent commit, so I re-used it here.

I was also considering just adding a newline between deprecations of different types (regardless of whether or not there is a too_many_warnings_message. Currently deprecation messages are stored in a hash of deprecation type => array of messages and we just flatten all the values to print them, but we could easily iterate over the keys and add newlines after each deprecation type.

What do you think?

cc @myronmarston