Semantic versioning and leading zeros about ensmallen

[conradsnicta]

This is why the minor version in Armadillo is always 100 or greater. (it's bounded to be between 100 to 999). This is consistent with semver guidelines -- it simply adds a further (logical) and minor restriction.

X.0 releases are always suspect anyway, so it's better to avoid them :)

[rcurtin]

Clearly not all brain cells were firing correctly when I opened this. Let's just do that then, although I'd prefer to got with 10-99, since I really doubt we'll ever have more than 89 minor versions. 👍