fix(builtin/README): update documentation

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(builtin/macros): comments

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel/universe_constraints): add new class for managing universe constraints

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel): use new universe contraints in the environment, allow new constraints to be added

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel): add get_universe_distance method

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean): bug in pop::context command, and add new tests for the universe command

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>