Can `BTags` search by the python class name?

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Hello, @junegunn . First of all thanks very much for your fzf plugin, It greatly facilitates my life.

When I write the python in nvim, I want to see all methods of a class, so I want to search the method by the classname. But When I use the `BTags`, It only can search the tag by name. Can it search based on the class name in [{tagaddress}](http://ctags.sourceforge.net/FORMAT)?

For example, I have a python file like this:

```
class Klass:
def method1(self):
pass

def method2(self):
pass
```

When I type the `BTags Klass`, It will show 3 tags, include `Klass`, `method1` and `method2`, not only the `Klass`.