Scheduled weekly dependency update for week 03

fix empty block handling

Avoid BlockDoesNotExistsException on `blockchain.stream()` and `Block()`
with `only_ops=True` on blocks without ops.
Fixes #149.

Scheduled weekly dependency update for week 01

* Improve file reading for beempy sign and broadcast
* add option to write file for beempy sign

This reverts commit b86e513f.

* Improve file reading for beempy sign and broadcast
* add option to write file for beempy sign

Scheduled weekly dependency update for week 52

add missing prefix to comment_options op

fix beempy verify --use-api

fixes #137

Update installation.rst

connect for beempy createwallet

The shared `Steem` instance does not connect by default.`beempy createwallet` raised a `beemapi.exceptions.RPCConnection: RPC is not connected!`. `wallet.keyStorage.getPublicKeys(prefix=self.steem.prefix)` tries and fails to lookup the network prefix in the unconnected state.