v1.8.0

Changed

• Requires Elixir >= 1.3
• Updated C4 contribution process to RFC42
• Updated timex dependency to 3.0 (Svilen Gospodinov)

Fixed

• Same task could be generated multiple times in a cluster (Po Chen)
• Elixir 1.3.0 introduced unsafe var warnings (Jamie J Quinn)
• Typo in README (Uģis Ozols)
• Code coverage below 100% (Lucas Charles)

Removed

• Unused alias (Philip Giuliani)