prefix is checked in getPublicKeys

* unit tests added for all new functions

Scheduled weekly dependency update for week 46

block.py: handle .block_num for get_ops_in_block

Fixes #122

* pep8 formating improved
* Too Many Requests error handled
* different limit handling in WLS fixed for account history
* percent-steem-dollars and max-accepted-payout added to beempy post

Scheduled weekly dependency update for week 44

* New anyx.io node added to nodelist
* GetWitnesses fixed

Scheduled weekly dependency update for week 43

* GetWitnesses added to witness

Improve documentation

Account
* update_account_keys added for changing account keys
* comment fixed for chains without SBD
RC
* RC changes from 0.20.6 included
Witness
* Fixed for chains without SBD symbol
Operations
* Claim_reward_balance fixed for chains without SBD symbol

Chains
* VIT fixed