Pycoin

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* fix crasher due to openssl version on Mac OS
* fix problem with blockcypher provider
* add support for keywords sig_hash_types_to_try, signature_hints_for_public_pair to solver
* add support for generating Digibyte addresses
* update to modern LTC address
* build with pyproject.toml

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* fix problem with recid > 1 (probably, hard to test)
* fix problem on Windows
* add Chaucha, STRAT
* fix Dogecoin bip32 prefix
* add documentation for pycoin.networks.Contract.Contract class

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* all API moved under pycoin.symbols.*.network
* rewrite of ecdsa package
* change how ScriptNullData works (arbitrary data now allowed after OP_RETURN)
* first crack at documentation
* added b58, coinc, keychain command-line tools
* removed obsolete genwallet, spend, and bu tools
* "netcode" renamed to "symbol"
* many, many other changes, big and small

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* remove support for (now obsolete) blockr.io
* change intbytes to use six-style names
* add BlockchainInfoProvider.tx_for_tx_hash
* add BECH32 segwit address support (including to ku)
* add msg tool (to generate and verify signatures)
* remove fetch_unspents tool (use tx -i)
* remove cache_tx tool (use tx -C)
* remove BlockHeader (functionality has been rolled into Block)

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* tx cmd will no longer use split pools unless an output is manually specified
* more refactoring of vm classes
* first crack at Sphinx documentation
* fix https://github.com/richardkiss/pycoin/issues/224
* fix https://github.com/richardkiss/pycoin/issues/225
* fixed recipes

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* respin build to fixing a problem with "vm.py" being named "VM.py" in
the 0.75 tar.gz file on pypi