crul v0.3.6

• Note: This version gains support for integration with
  webmockr, which is now on CRAN.

NEW FEATURES

• New function auth() to do simple authentication (#33)
• New function HttpStubbedResponse for making a stubbed
  response object for the webmockr integration (#4)
• New function mock() to turn on mocking - it's off by
  default. If webmockr is not installed but user attempts
  to use mocking we error with message to install
  webmockr (#4)

MINOR IMPROVEMENTS

• Use gzip-deflate by deafult for each request
  to make sure gzip compression is used if the server
  can do it (#34)
• Change useragent to User-Agent as default user
  agent header (#35)
• Now we make sure that user supplied headers override the
  default headers if they are of the same name (#36)