Rather than introducing a custom macro, this commit opts to implicitly
configure the snippets attribute instead. The attribute is configured
will the path into which snippets are generated, relative to the
directory that contains the Asciidoctor document that is being
rendered.
The samples and documentation have been updated to use the new
spring-restdocs-asciidoctor module and the implicitly configured
snippets attribute.
Closes gh-297
Rather than requiring an output directory to be explcitly configured,
a default is now automatically configured based on the build tool
that's being used. When using Gradle, snippets will be generated in
build/generated-snippets. When using Maven, snippets will be
generated in target/generated-snippets.
See gh-297
