Section 11: A larger set of pre-release is higher

Clarifies the comparison between, eg 1.0.0-a vs 1.0.0-a.b
Attempt to clarify precedence even more.

While this is implied, SemVer never really makes it clear that
1.9.0 < 2.1.1. It only specifies how each identifier is compared.

This commit attempts to clarify how the comparison of each identifier
relates to the comparison of the whole version.
Merge pull request #108 from mojombo/clarify-version-comparisons

Clarify version comparisons