Auto-load API version

[Unix-Code]

Changes

• Client now has version field (for easy access)
• Client auto-loads api version and falls back to manual DEFAULT_API_VERSION or an override if present
  • This should ideally lead to the library (us) not maintaining the default API version anymore (though this would require an actual fallback of some kind or an error)
  • Auto-loading should be skippable if a version override is given or auto_load_api_version is set to False in the constructor
  • Auto-loading parses the api result here for a version string

Notes

• The httpretty v0.7.2 doesn't seem to actually function in newer versions of python, so the latest version compatible with python 2 should be httpretty v0.9.7 - this fixes an SSL error

[bennylope]

Thanks, this is live on PyPI now!