Matchers do not match base classes

In
```Python
import libcst as cst
import libcst.matchers as m

m.matches(cst.SimpleString("'foo'"), m.SimpleString) # True
m.matches(cst.SimpleString("'foo'"), m.BaseString) # False
```
I expect both statements to be true. Otherwise, you need to use `OneOf` or `|` on all string types. The same applies for numbers.