ENH: enhance query syntax
#### Is your feature request related to a problem?

No, it's additional behavior.

#### Describe the solution you'd like

```df.query(key=value)```

Add new query behavior for simple key lookup. Helps improve readability.

#### API breaking implications

Will not break API. Make the query expression optional, new calls hit this feature if and only if the query expression is not provided.

#### Describe alternatives you've considered

Just not adding this. It's sugar and adds some complexity.

#### Additional context

Single value lookups can be:

```
info = df[df['zipcode'] == adress.zip]
``` 

Or if you want to use the query API:

```
info = df.query(f'zipcode == {address.zip}')
```

I've found myself writing (on accident)

```
info = df.query(zipcode=adress.zip)
```

The third approach is cleanest and easiest to read. The first approach (via bitmask) is fastest. We can just short-circuit the new special case to use a bitmask, rather than going through the "query" machinery each time.