remove 'private' from src/core/CMakeLists.txt link_libs
Merge pull request #114 from da2ce7/fix_cmake_private

Fix CI build: remove 'private' from src/core/CMakeLists.txt link_libs
remove unused (for now) 'bitcoin-crypto' submodule
add crypto++ submodule and build
move to crypto++ zlib
move to crypto++ base64
replace openssl hash with cryptopp