Add RequestSigner class
Add Faraday RubyGem as a dependency

Downgrade Faraday to 0.8.9 to be compatible with VCR
Add VCR RubyGem as a development dependency
Add Pete::Client#connection
Parse JSON in responses using Faraday middleware
Add Faraday middleware for request signer
Add health check API
Use SVG badges in README where available