Finish porting docs to mkdocs

Changes

• Finish porting docs to mkdocs

Crystal `1.0.0` compliance

Changes

• Updates crystal version to be installable in Crystal versions greater than 1.0.0

Choice Constraint & Better mock validators

Additions

• Add Choice constraint

Changes

• Make AVD::Spec::MockValidator and AVD::Spec::MockContextualValidator classes, and allow setting the violations at instantiation or at runtime via a setter

Crystal 1.0.0-pre1 updates

Fixes

• Be more specific on abstract def interfaces to be compliant with crystal-lang/crystal#9634

Initial Release

• Initial release