Update design_persona.md

merged additional text (reference to mailchimp styleguide) from voice_and_tone.md
Delete voice_and_tone.md

now contained in design_persona.md
Create style_guide.md

Creating or editing summaries of divisions or policies for Public Whip? Use our style guide. 
It's a starting point.
Update style_guide.md

added examples & fixed some formatting.
add link to Open Gov 2.0 licence.

link to Open Government 2.0 licence https://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/
added active voice example
minor formatting changes for scanning page

made headings after "you should" smaller - and made all headings after that one complete the sentence beginning you should. eg. "use common words" becomes you should ... use common words
minor formatting changes/corrections

Write for the web bigger + corrections
Move style guide and make it accessible via the app
Strip trailing spaces only
Set page title
Don't repeat project title
Bump headings up a level and make them consistent

It's the only content on the page so it can start with an h1
Clean up extra lines only
Consistently don't use title case for h2s

They seem more conversational on this page so that seems appropriate
Fix display of bulleted lists
Fix typos
Add link
Split new list item
Hyphenate word and change dash style