Bitcoinlib

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* Cache transactions and address info retrieved from Service providers
* Increase efficiency when updating transactions
* Fix path issues in Windows
* Disable Python 3.4 support, add 3.8 tests
* Fix several transaction update issues

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* Enable database backup
* Fix documentation build
* Review all documentation
* Add Jupyter manual
* Add various unittests
* Fix issues with service providers
* Fix many minor bugs

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* Add support for bcoin client
* Add support for mysql and postgresql databases
* Add blockstream, bitaps and smartbit provider
* Improve scan and update transaction methods
* Remove obsolete providers
* Fix bitcoind and litecoind issues
* Fix various provider issues

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* Fix pip install on some platforms

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* Add many unittests and increase coverage > 90%
* Update documentation, docstrings
* Rewrite HDWalletTransaction classes
* Improve bitcoind Service client
* Partially remove blockexplorer support and unittests
* Improve database update scripts, add version numbering

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* Improve and speed up use of ECDSA cryptography methods
* No private keys in json and dict outputs by default
* Bugfixes, PEP8 fixes and docstring updates