Added webhook and webhook events management api support, parsing webhook event support and verifying webhook events which is done via pyopenssl, updated samples, tests and documentation
four spacing indentation for tests
Merge branch 'webhooks'

Merge in webhooks branch for 1.6.0 release
Merge branch 'master' into stable

Merge in master for 1.6.0 release
Update travis, coveralls and user agent
Merge branch 'master' into stable

Merge in travis and coveralls badge updates and user agent