Remove README files that have been since been migrated to the reference
documentation. Also updated remaining markdown files to asciidoctor to
save having a mix of different formats.
Fixed gh-503
Add a gradle `ResolutionStrategy` that resolves missing version numbers
using the `spring-boot-dependencies` POM.
This commit also introduces a new `spring-boot-dependency-tools` module
that provides programmatic access to the `dependencyManagement` section
of the dependencies POM.
Fixed gh-262
