Improve the markdown output for release notes

 - Fix rendering of links (the URL and hypertext were transposed)
 - Limit commit message to 80 characters
 - Fix conversion of markdown bulleted lists to render nested lists
   correctly on scala-lang.org (needs a preceding newline and just
   two space indent, unlike the markdown flavour we have in this
   project that needs *no* preceding newline and a four space indent.)
   Sigh.
Merge pull request #26 from retronym/release/2.10.3-markdown-prettify

Release/2.10.3 markdown prettify