Connection class now has remote_copy and more

What's Changed

• Added remote_copy and other changes by @JacobCallahan in #2

Added:

• Connection now has a remote_copy method to copy files between connections

Changed:

• Updated pyo3 to 0.21
• Made minor changes to types to adjust to pyo3 0.21
• Simplified aquiring sftp on a connection

Removed:

• Dropped Cargo.lock from git tracking

Full Changelog: 0.1.1...0.1.2