Refactor/Simplify Envar.get/2 to avoid excessive nesting #22 (Thanks @SimonLab!)

v.1.0.9

Minor refactor to Envar.get/2 - non-breaking. #22

Lint code + improve docs. No code changed.

v1.0.7

Docs + Lint release. No code changed see: #16 thanks to @SimonLab

Extend Envar.get/1 to Envar.get/2 which allows a default param.

v1.0.6

Extend Envar.get/1 to Envar.get/2 with default param. Thanks to @tomk…