feat(library/tactic): add apply_tactic

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add back (backtracking) command

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/tactic): add disj_tactic

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/tactic): rename boolean.* to boolean_tactics.*

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel/replace_visitor): check interrupted flag and stackoverflow

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean): check wheter the synthesized proof term has metavars or not

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