bigger codebase for benchmarks

[adriaanm]

(but, concern with jitter)

[lrytz]

• Include library / reflect / compiler
  • Since it's hard to keep a stable codebase for a very long time, we need a mechanism to get a source snapshot depending on the scala version being benchmarked
  • In the graphs, have a separate series for each version of a codebase
• Check the community build for other projects that could be built, e.g., parts of akka

[lrytz]

The core of this is done, corpus is versioned and library / reflect / compiler is in there. Still might need some refinements in the graph, this can come at its time.