Assisted digital personas

- Add content to assisted digital user research page
- Add associated user persona documents
Remove .html from links
Reflect the name of open document format standard

See https://www.gov.uk/government/news/open-document-formats-selected-to-meet-user-needs
Remove custom li style on Digital by Default page

As requested by various people.
Be explicit with the return type
Extract function to lint

Shorter function, split out parsing and result handling.
Merge pull request #436 from alphagov/remove-dbd-intro-list-style

Remove custom li style on Digital by Default page
Minor tweak for lint output
sever typo

ooh my git commit title has a double meaning
Merge pull request #437 from alphagov/sever-typo

sever typo
Update README to reflect it’s now a sinatra app
Update README

Running Sinatra by itself won't reload the service manual changes.
You'll need to run that manually.

We can improve this at some point.
Merge pull request #438 from alphagov/update-readme

Update README
beta and alpha banner guidance, plus link to index
get rid of white space
Change href text
Merge pull request #432 from alphagov/assisted-personas-

Assisted digital personas
Merge pull request #439 from alphagov/alpha-beta

Alpha beta
Merge pull request #434 from alphagov/cleanup

Use the correct document name
Alter travis config to cache gems

We sometimes see failures to connect and download gems. This is
annoying.

Setting this now so that we can take advantage of it if the feature
is ever rolled out to the free tier.