feat(library/standard): add bit, char, and string types

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/parser): bug when parsing identifiers

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(util/hash): relax pre-condition

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/tactic): add namespace 'tactic', improve expr_to_tactic failure error message

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

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