Fixed #35, paragraph CSS is now output correctly.
Switched summary links to serif.
Fixed #32, smaller margin between chapter heading and intro. Also tidied vertical rythym throughout.
Added some comments.
Merge branch 'feature/fix-intro-heading-margin' into develop
Improved css message styling.
Switched .code to .code-inline and .code-block.
Merge branch 'feature/split-code-classes' into develop