14 months ago ago adjust position according to offset of command/exec id;
14 months ago ago clarified signature;
2015-03-13 ago simplified Command.resolve_files in ML, using blobs_index from Scala;
2015-03-12 ago tuned -- more uniform ML vs. Scala;
2014-11-06 ago more explicit Keyword.keywords;
2014-08-12 ago separate module Command_Span: mostly syntactic representation;