Update versioning scheme

[mtomko]

PoolQ should use a versioning scheme like W.X.Y.Z. The W version for PoolQ 3.x should be considered 3; this represents a significant milestone in PoolQ implementation or functionality. The remaining X.Y.Z versions should follow a basic semver versioning scheme.

I propose this because the 3 version of PoolQ represented a significant and meaningful change in PoolQ. Making a major version change to PoolQ now and following semantic versioning would pose communication problems with collaborators or other users of PoolQ. Adding a W version lets us freeze that most-significant digit while allowing us to follow proper semantic versioning in all other ways.

[mtomko]

Note, semver may not allow W.X.Y.Z but Haskell Package Versioning Policy does, and that policy may work for our needs. Notably, it is also supported by SBT.