func_kw_complete for builtin and cython with embededsignature=True using docstring

```pyton
np.array([1], su
```
has subok= in completion

```pyton
min(k, k
```
has key= in completion list or

Cython embded signature works too ( http://wiki.cython.org/enhancements/compilerdirectives ) May be embded signature should be default in %%cython magic?
```
@cython.embdedsignature=True

def cython_func(a, mykwd=''):
    return mykwd
```
When you do
```
cython_func(a, my
```
has mykwd= in completion list


For Cython constructor, it's a little bit tricky since the constructor signature is put in class docstring not __init__. But, it's working
```
@cython.embdedsignature=True

class MyClass:
    def __init__(a, awesome_argument=1):
        pass
```

```
a = MyClass(a, awe
```
has awesome_argument= in the completion list too