[WIP] Clean up Attribute::Builder
Extract attribute extensions into separate files
Introduce Attribute#finalize
Make sure coercer is always injected and simplify attribute extensions
Remove obsolete options
Extend Attribute.build specs
Add specs for Attribute#coercible?
Add specs for Attribute#lazy?
Add specs for Attribute#value_coerced?
Add missing @api tag
Allow using String/Symbol type names
Add example to Attribute.build spec
Add missing specs for Virtus#attribute
Add missing specs for Attribute::Hash
Add missing specs for Attribute::Collection
Add specs for Attribute#set_default_value
Add missing scenario for Attribute#get spec
Add specs for Boolean#value_coerced?
Add specs for Attribute.coerce
Extend spec for Virtus.attribute with a module example