- A new `Vault::InvoiceBuilder::Client` can be used to easily get
  rendered HTML for a given receipt.
- Add a README that describes how to use the new client.
- Add Git ignore file, Yard configuration, Rakefile, Gemfile and
  gemspec files.
Merge pull request #1 from heroku/bootstrap-project

A new Vault::InvoiceBuilder::Client can be used to easily get
rendered HTML for a given receipt.

Add a README that describes how to use the new client.

Add Git ignore file, Yard configuration, Rakefile, Gemfile and
gemspec files.