v0.5.16

1. follow up ehtereum/solidity v0.5.16;
2. about swarm hash: source filename irrelevant metadata;
3. delete token units szabo and finney;
4. tune some build scripts.

For docker images, find youchain/solc in docker-hub.

v0.4.26

1. Base on the ethereum/solidity v0.4.26;
2. Change some units name;
3. Change default evmVersion to Constantinople;
4. Delete the op code DIFFICULTY.