Constants segregation and address refactor

Added

• New way to create addresses from scripts
• Many test vectors on SegWit-over-P2SH address generation
• All Bitcoin-related constants have been moved to a separate file for better code readability and easier forking by other coins

Fixed

• Ambiguous semantics between address() and to_address() in scripts

Backward compatibility

• The to_address() method in scripts no longer exists