transferec: securely send file

Open Source LAN file transferring tool.Secure transferring is achieved via cert pinning.The mobile app generates self-signed certificate by itself and then serves HTTPS for other machines to upload to it or download from it.By scanning QR code, the SHA256 (in base64) hash of cert can be used for cert pinning so it prevents MITM attack.Desktop/server machines (even without desktop environment) can connect to mobile device with curl --pinnedpubkey. More info can be found at https://github.com/cshu/transferec