index.rst: fix blockchain example

Discussions
* Replies_by_last_update and Trending_tags
Blockchain
* get_transaction_hex added
Account
* get_tags_used_by_author added
Docs
* apidifinitions added

beemapi/Nodes
* add option to freeze a node, in order to prevent switching to the next node

ImageUploader can be used to upload an image file or an image in bytes

Scheduled weekly dependency update for week 24

Account
* get_feed_entries, get_blog_authors, get_savings_withdrawals, get_escrow, verify_account_authority, get_expiring_vesting_delegations
* Documentation improved
* Account parameter handling improved
Blockchain
* get_account_reputations added

Blockchain
* thread_limit parameter removed
* batch_mode set to True for threaded blocks()
* block sanity check added for threaded blocks()

Blockchain
* Check if all block could be fetched added
* Thread and Worker class for block fetching added

* Unit test for issue #27 added
* Exception handling added to blocks using threads
* get_all_accounts fixed for appbase calls

Block
* fix missing identifier
* fix change trough json_transactions
Blockchain
* Check for missing blocks added to blocks with threads

Account
* _parse_json_data improved and all missing ints and dates added
* json() adapted to _parse_json_data()
Block
* _parse_json_data added, expiration and timestamp are now datetime objects
* property json_transactions and json_operations added, which return trx and ops with date strings
* BlockHeader improved and datetime parsing added
Blockchain
* adapted to new datetime objects
CLI
* adapted to code changes
Comment
* int and dates inside active_votes are parsed
* Missing dates and int are parsed
Market
* date parsing to datetime added to market_history
Vote
* Some improvements
Witness
* _parse_json_data added
* all date and ints are parsed
* Demo added to Witnesses, WitnessesVotedByAccount, WitnessesRankedByVote and ListWitnesses 
beemgraphenebase/types
* datetime handling added to PointInTime
Unit tests
* test_account adapted
* test_export added to test_block
* test in test_comment fixed
* test_export added to test_witness

Account
* lazy and full are correctly passed
* _parse_json_data() added to parse json
Block
* lazy and full are correctly passed
* empty operations are handled
* op_statistics improved
Blockchain
* virtual ops and ops statistics are seperatly calculated
Comment
* _parse_json_data() added to parse dates and amounts
* author_reputation is parsed to int
* lazy and full are correctly passed
Vote
* lazy and full are correctly passed
* _parse_json_data added to parse date and rshares and reputation
* vote.time is a datetime object
* json() returns the original string
Witness
* lazy and full are correctly passed
GrapheneRPC
* time_limit removed, as it supresses KeyboardInterrupt
* ws.settimeout() is set for websocket
* WebSocketTimeoutException  handling added
Unit tests
* test_account fixed
* test_time_limit removed from test_steemnoderpc
* checks added to test_blockchain_batch

Documentation updates