Anonymised paper build omitting appendices

[rolyp]

Build script and macros to build submission version:

• collate-examples.sh to run optionally (but always on GitHub), snapshot of examples in repo
• macro for proof references difficult – see note below
• two orthogonal conditionals: anonymous and appendices (although we only need 3 of the 4 cases)
• set anonymous whenever @ACM@anonymous is set
• macro for language name
• options for build.sh, with default
• GitHub Action to build all configurations
• submission version to enable review option (for line numbers)

[rolyp]

Not sure how to implement a macro which conditionally includes a proof environment. The long-hand is:

\ifappendices
   \begin{proof}
   \appref{proofs:core-language:eval:gc:bwd-after-fwd}
   \end{proof}
\fi