Adding AWS Lambda proxy integration

Supporting HTTP proxying to lambda functions.

Just that simple:

const gateway = require('fast-gateway')
const server = gateway({
  routes: [{
    proxyType: 'lambda',
    prefix: '/service',
    target: 'my-lambda-serverless-api',
    lambdaProxy: {
      region: 'eu-central-1'
    }
  }]
})

server.start(8080)