blockchain.stream and blockchain.ops are missing virtual operations

Expected behavior

blockchain.stream() and blockchain.ops() should stream both regular and virtual Steem operations. Via optional arguments, it should be possible to stream only virtual operations.

Actual behavior

blockchain.stream() and blockchain.ops() only stream regular operations. Virtual ops like author_reward, curation_reward and others are not contained in the stream.

blockchain.ops() lists an optional parameter only_virtual_ops. If set, blockchain.ops() fails with

TypeError: blocks() got an unexpected keyword argument 'only_virtual_ops'

How to reproduce

from beem import Steem
from beem.blockchain import Blockchain
s = Steem(node='https://rpc.buildteam.io')
b = Blockchain(s)
for op in b.stream():
    if op['type'] == "author_reward":
        print(op)
        break

This script never completes, because none of the ops yielded by stream() is a (virtual) "author_reward" op.

The same code with steem-python completes within seconds:

from steem import Steem
from steem.blockchain import Blockchain
s = Steem(nodes=['https://rpc.buildteam.io'])
b = Blockchain(s)
for op in b.stream():
    if op['type'] == "author_reward":  
        print(op)
        break

Stacktrace for virtual_ops_only

>>> from beem.blockchain import Blockchain
>>> b = Blockchain()
>>> for op in b.ops(virtual_ops_only=True):
...     print(op)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/site-packages/beem/blockchain.py", line 323, in ops
    for block in self.blocks(start=start, stop=stop, **kwargs):
TypeError: blocks() got an unexpected keyword argument 'virtual_ops_only'

Environment

# python --version
Python 3.6.4
# beempy --version
beempy, version 0.19.26
# steempy --version
steempy 1.0.0