Beem

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* Add HIVE chain
* improve hive chain detection
* add hive option to nodes in Nodelist
* new is_hive property of steem object

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* Fix non ascii text handling on some nodes
* Add STEEM_REVERSE_AUCTION_WINDOW_SECONDS_HF21 constant
* Fix get_curation_rewards

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* First release for HF21
* get_downvoting_power added to account
* get_downvote_manabar added to account
* add options use_tags_api to use database api to get comments
* fix get_similar_account_names
* add more try expect to fail back to condenser api
* operations for account_update2, create_proposal, update_proposal_votes and remove_proposal were added
* update_proposal_votes was added to steem
* update_account_jsonmetadata was added to account
* new beempy delete were added

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* Switch to next node, when current node has the necesary api not enabled
* handle Client returned invalid format. Expected JSON! and switch to next node
* More checks added
* get_estimated_block_num is faster and uses BlockHeader
* exclude_limited=False is default now for get_nodes

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* Fix 195 - comment.downvote(100) will now downvote with 100%, negative numbers are not allowed anymore
* comment.upvote(), negative numbers are not allowed anymore
* Fix 193 - steem.vote() was added, so that voting is possible without tags_api
* PR 181 - improve permlink derivation by crokkon
* PR 192 - fixes compatibility issues with WhaleShares HF2 / v2.5 by alexpmorris
* Fix bug for get_estimated_block_num when a block is skipped

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* Fix float entered in Amount will be reduced by 0.001 due to rounding issues
* fix Amount.amount and added Amount.amount_decimal
* Prevent that wrong reputation in a Comment API answer break the Comment object