tap_int

An implementation of freertr's tapInt in Rust using the
libc and nix crates.

Improvements to the original:

clearer CLI arguments
the ability to add multiple IP addresses easily
full IPv6 support
clearer error messages
support for daemonizing
support for resolving hostnames
optional support for encryption (using the XChaCha20Poly1305 algorithm) using the orion crate.


Usage:
 --iface_name <str>      Name of the interface
 --laddr <socket addr>   Listen address
 --raddr <socket addr>   Remote address
 --addr <ip addr>        Address to add to the interface (in CIDR format)
 --daemonize             Run as a daemon

 --addr can be used multiple times to add multiple addresses to the interface
 ```

### Features
- `crypto`: encryption using XChaCha20Poly1305. The key must be 32 bits long, and should be the same on both sides of the tunnel.