DOC: Warn the user when they pass `default` to a TraitType....
DOC: Warn the user when they pass `default` to a TraitType.
Most TraitType subclasses accept a `default_value` parameter. On more
occasions than I care to admit, I've written something like:
```
class Foo(HasTraits):
foo_int = Integer(default=5)
```
when what I actually meant was
```
class Foo(HasTraits):
foo_int = Integer(default_value=5)
```
I suspect I'm not the only one who's had to track down this same bug
multiple times.
