Unexpected parentheses required when using multiple WHERE conditions
Peewee leans on pythons parser to generate expressions. Because of pythons operator precedence you need parentheses around most comparisons. No magic here, just python.
 And yet I can do this without needed extra parens:

```
.where(
    (modelObject.field_name << ['a','b','c'] |
    modelObject.field_name % "%word%")
    )
```

Seems inconsistent. I think this needs to be explained in the docs. At least "you should use parentheses around all comparisons, just to be safe." But a list of situations would be ideal.
 What do you suggest? Best practice is just put parentheses around binary expressions, then you won't have any issues.
 You can created the equivalent expressions by calling the appropriate doubles underscore method on the field object. You can also instantiate expression objects by hand.
 The use of parentheses in your python code won't affect the SQL being generated, improves readability for complex, mutli-clause queries (as I typically assume you line-break each expression), and leaves no room for error.

http://docs.peewee-orm.com/en/latest/peewee/querying.html?highlight=precedence#expressions
 Sorry, I think you've already got a note in the docs to this effect.

> Note that the actual comparisons are wrapped in parentheses. Python’s operator precedence necessitates that comparisons be wrapped in parentheses.

Thanks for your additional thoughts on this solidly closed issue.

I would expect to be able to write:

```
where(
    (
    modelObject.field_name.is_null(True) |
    modelObject.field_name == ""
    )
)
```

but I must add parentheses around `modelObject.field_name == ""` or the query will be generated improperly. The improperly generated query is essentially

```
WHERE `t1`.`field_name` IS NULL = ''
```

which is exactly the opposite of what I want, returning all records that are not null.

For more discussion, please see:
http://stackoverflow.com/questions/33905987/why-is-peewee-not-nesting-this-where-clause-correctly/33906132
