Dnscrypt Wrapper Versions Save

See https://github.com/cofyc/dnscrypt-wrapper/blob/master/CHANGELOG.md#v042.

See https://github.com/cofyc/dnscrypt-wrapper/blob/master/CHANGELOG.md#v041.

See https://github.com/cofyc/dnscrypt-wrapper/blob/master/CHANGELOG.md#v040.

• XChaCha20 supported
• a lot of tests added
• and many bug fixes and improvements

Thanks to @jedisct1 @chantra @aureq @xdel @rampageX @AMDmi3.

• remove GPLv2, release under the ISC license
• update example secret key / cert, etc
• fix compiler/linker flags handling

• Rename --provider-publickey-fingerprint to --show-provider-publickey-fingerprint. It's more conventional to use a verb if you want to do some action, like gen-provider-keypair.
• Use TCP_QUICKACK instead of TCP_NODELAY if available (Linux 2.4.4+) See https://news.ycombinator.com/item?id=10608356
• Send a short packet with TC set if the query_len < response_len
• Support sending server cert over tcp
• Use the certificate timestamp as a serial number instead of a fixed serial.
• And some other minor fixes.

Import argparse sources files directly.

• Crypt public key is not required, see README.md for detail instructions. (#47)
• Support multiple crypt secret keys. (#49)
• And many other improvements.

All thanks to @jedisct1 !

1. Add debug facilities to log stack trace in case of segment fault.

Tons of improvements from Frank Denis.