Replace `%eq(a, b)` with:
* `a <-> b`: unify two logic variables
* `a <- b`: assign a value to a logic variable
Replace `%eq(a, b, conv_prop=N.p)` with:
* `a <- N.p%(...)`: assign a value to a logic variable after a
conversion/combination using a property from 1) one or multiple logic
variables or 2) an entity:
Replace `%predicate(N.p, ...)` with:
* `N.p%(...)`: create a predicate atom from a property, several logic
variables and optional extra arguments.
This commit introduces full support for dynamic variables in Lkt:
* new syntax for declaration: `dynvar my_var: MyType`;
* new annotation to require it at property call:
`@with_dynvars(my_var)`;
* associated unparsing and lowering code.
