test: Add (failing) test for declarative options

See #66

[ci skip]
feature: Allow use of snap-opt-* attrs for opts
test: Make sure variable values can be used w/ snap-opt-* attrs
docs: Add info about snap-opt-* attributes
test: Add test for dynamic snap-opt-* attrs

[ci skip]
test: Fix typo... jasmin is not defined
feature: Add binding for snap-opt-* attrs
docs: Note that snap-opt-* attrs have 1way binding
chore: Bump version for release (v1.7.0)