First rough draft
Tweaks "return codes" section following Pedro's comment
Details on versioning, i18, multi-tenancy
Adds TOC, fills first sections
Notes on HATEOAS
Notes on intrinsic-ness
Rationale for index endpoints
Adds conciseness as a principle
Adds note on mobile corner case
Adds JSON-HAL as the standard format
Adds discussion on pagination
Adds reference links
adds notes on modeling/associations
Adds i18n discussion and index example
New version after work from the Arch panel
Adds PATCH clarification
Merge pull request #20 from HouseTrip/api-principles

API guidelines (final version)