Create a version for supporting solidity compiler 0.8.0+

[douglasqian]

As titled, this issue is about supporting a version of this library that's compatible with solidity compiler versions 0.8.0 and above so newer contracts can integrate with this library

cc: @bowd

[douglasqian]

Would love to help with this, wonder if the easiest thing to do is to create a src/0.8 directory for this?