Support multiple tagging schemes: v2, v2.4, v2.4.6 or v2.4.6.8

[rudymatela]

Currently Hoff supports "merge and tag"ging for when versions are simply a "v" followed by an integer:

• ... v29, v30, v31, v32...

We could perhaps make it so that Hoff supports other tagging schemes, such as SemVer (v1.2.3) or Haskell's PVP (v.1.2.3.4).

For SemVer:

• "merge and tag" would increment the patch level: v2.4.6 -> v2.4.7;
• "merge and tag minor" would increment the minor level: v2.4.6 -> v2.5.0;
• "merge and tag major" would increment the major level: v2.4.6 -> v3.0.0.

For Haskell's PVP:

• "merge and tag" would increment the patch level: v2.4.6.8 -> v2.4.6.9;
• "merge and tag minor" would increment the minor level: v2.4.6.8 -> v2.4.7.0;
• "merge and tag major" would increment the major level: v2.4.6.8 -> v2.5.0.0.
• "merge and tag principal" would increment the principal "major-major" level: v2.4.6.8 -> v3.0.0.0.

Which versioning scheme is being used could be autodetected from existing tags.

And initial implementation could be just picking up incrementing the patch level by default (the last number) followed by one that implements the extra commands.

(I got the idea for this improvement from a private conversation with @fatho.)