Add Rake task for generating changelog entries

[pyrmont]

This commit adds a Rake task to assist in writing CHANGELOG updates. The task generates messages using the first line of the commit message. It automatically inserts links for references that begin with # as well as providing a heading and a link to compare against the previous version.

[pyrmont]

@gfx It doesn't completely automate things but this does part of what you were talking about wanting :)

[gfx]

Awesome!! You are the hero! 🚀

[ashmaroli]

@pyrmont If you're looking for automation, there might be a GitHub App that creates a changelog entry every time a PR is merged..

[pyrmont]

@ashmaroli Yeah, for future automation efforts something like that might be preferable. The way CHANGELOG works currently, the individual entries need to be sorted by lexer (or otherwise in general) and that requires a human editor. The purpose of this Rake task is to really get most of the busywork done in terms of formatting the individual entries.

[ashmaroli]

@pyrmont Any reason why you opted to chain with a trailing dot instead of a leading on the newline?

def prev_version
  @prev_version ||= @repo.tags
    .select { |t| t.name.match?(/^v\d+\.\d+\.\d$/) }     # Ruby 2.4 String#match? ?
    .map { |t| t.name.slice(1..-1).split(".").map(&:to_i) }
    .sort { |a, b| sort_versions(a, b) }
    .last
    .join(".")
    .prepend("v")
end

[pyrmont]

@ashmaroli Just that I am an idiot :P