Tidy up roadmap, edit some text for clarity

The roadmap is now tidied up with many cosmetic changes and the text has minor edits. The README points to the updated PNG file. However, the PNG translation from the spreadsheet is not perfect.

Accordingly, have also included a PDF file of the roadmap , which translates more accurately from the spreadsheet, and a small .md to test how well the PDF roadmap is rendered on github within a markdown file.

Subsequently we can remove either the PDF or PNG whichever renders with lesser quality.