Apply prettier to markdown and html files

[pvspain]

Thanks for accepting prettier Dave @dwmkerr. I'm no formatting nazi, but I've found without a common team style logical changes have a tendency to get lost among formatting diffs and there can be many false positive diffs due to only formatting.

chore

• Extend scope of eslint to package root and sample folders.
• Add new scripts to package.json (prettier, prettier:fix) to enable prettier to be run on markdown and html files.

doc

• Tweaks to documentation by prettier
• html fixup in sample/index.html detected by prettier

[dwmkerr]

Looks good to me!