Drop Python 3.5 support − Migrate to hashlib.scrypt

#60 (closed): Drop Python 3.5 support

• CI: Raise container Python version to v3.6
• pyproject.toml: Set v3.6 as minimal supported version
• Update documentation

#86 (closed): Replace pylibscrypt.scrypt by hashlib.scrypt

• Specify parameters since they are mandatory
• Remove pylibscrypt dependency
• ScryptParams: pass attributes as mandatory since mypy is not happy because hashlib.scrypt has required keywords

Close #60 (closed), #86 (closed).