tasks should return XMLHttpRequest
fix tests
moved layer creation into a function so the renderers can override it when two layers are needed
basic setters for tasks
more task setters
revert change in spec
Merge pull request #344 from kneemer/move-layer-creation-into-function

moved layer creation into a function so renderer plugin can override it
Merge pull request #345 from patrickarlt/master

Refactor Tasks for easier maintenance
Update CONTRIBUTING.md
Update README.md
fix link to license
Merge pull request #347 from ngoldman/master

fix link to license