Merge pull request #15 from rthomas/master

Allow config overrides with environment variables
Update README.md
Fix package build version
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Adding text/plain request header to handler task API behaviour changes introduced in Marathon 0.7RC
 - commit reference in Marathon: https://github.com/mesosphere/marathon/commit/2fbee6984c1d655354d8ce99fce29822196954c7
Merge pull request #18 from QubitProducts/fix-parse-tasks

Adding text/plain request header to handler task API behaviour changes i...
Update README.md
Update README.md