Release 4.0.0

• Convert to cache class (#29) (e59bcef)
• update README and CHANGELOG with references to composition section (61be521)
• update CHANGELOG and final tweaks (2f0eead)
• add README documentation on composition (2f2ad45)
• various code improvements (d3cab64)
• clean up some types (0c42f7c)
• remove old benchmarks CSV (87e3510)
• update CHANGELOG and deprecate cacheSnapshot (2282773)
• update README (c87f087)
• update tests and types (5f45a33)
• working POC for cache class (ecd1476)