v0.12 Release

Changelog:

Enhancement(s):

• Added SetRetryWaitTime and SetRetryMaxWaitTime methods to set custom wait time PR #66 @bak1an
• Added SetCookieJar method to set custom cookie jar PR #69 @lrita
• Code improvements and streamline PR #71 @alexmontecucco
• Performance improvement buffer pool @jeevatkm

Breaking Change:

• Drop support for go1.2