Change version of user documentation from latest to pre-spec
In its current state, the user documentation for the AsciiDoc Language hosted in this repository constitutes the initial contribution for this project, which is a reading of AsciiDoc as implemented by Asciidoctor. The draft outline for the specification has set a course to formalize the language leading up to the 1.0.0 release. That means there will be notable differences in how the parsing is modeled and the language interpreted, which will require material updates to the explanations in this documentation. We need to preserve the user documentation in its current state, and flag it as such, for users of Asciidoctor while the spec is under development. In order to do so, the version of the user documentation in this repository should be changed from "latest" to "pre-spec". The documentation in this state can continue to accept refinements to the reading of AsciiDoc as implemented by Asciidoctor during this period.
Once we get to the point where we start updating the user documentation to match the specification, we'll create a pre-spec branch to store the pre-spec version, then update the version in the main branch to match the version of the specification.