Create Unique index fails
Oh, I see this is fixed in the Github version... Sorry.
 I'll push an update today or tomorrow

I'm using Peewee 2.0.2 (installed with pip), my model looks like this:

```
class Settings(Model):
    key = CharField(max_length=25, index=True, unique=True)
    value = CharField()
    vtype = CharField(max_length=6)

    class Meta:
        db_table = 'settings'
```

When I run `Settings.create_table()` the following error happens:

```
File "......./peewee.py", line 2008, in create_table
    for fields, unique in cls._meta.indexes:
ValueError: too many values to unpack
```

When I check Settings._meta.indexes, it has the following value: `['key']` - hence the error.

If I comment these lines out - everything works fine since the field indexes are added immediately before this code is executed:

```
if cls._meta.indexes:
    for fields, unique in cls._meta.indexes:
        db.create_index(cls, fields, unique)
```

I know that these code should add the indexes defined in the `Meta` class - but in that case the indexes defined in the model field definitions should not be appended to self._meta.indexes.
