--strict does not include all mypy checks

[TylerYep]

When configuring mypy, I mistakenly assumed that --strict included all possible mypy checks (thus being as strict as possible). However, there are a lot of other checks that are not included in --strict, such as --warn-unreachable or disallow_any_unimported = True or even enable_error_code = ignore-without-code.

Can we add a section to --strict's documentation and --help page explaining all of mypy's stricter checks that are not included in --strict? As far as I can tell, these are the missing ones:

[mypy]
strict = True

# Missing:
warn_unreachable = True
disallow_any_expr = True
disallow_any_decorated = True
disallow_any_explicit = True
disallow_any_unimported = True

# Not strictness checks per se, but enforces uniformity for type: ignores.
show_error_codes = True
enable_error_code = ignore-without-code

Additionally, it might be useful to add a --strictest flag that always opts into all of mypy's checks.