refactor(library/standard): remove parameter from 'tactic' inductive type

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): parse numerals as expressions of type 'num.num'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): parse numerals as expressions of type 'num.num'