a bit of cleanup on the relation
adding missing when, for mapThen / invokeThen
more cleanup, refactoring
moving all lib files into a 'dialects' directory
Merge branch 'master' into active-record

* master:
  moving all lib files into a 'dialects' directory
  more cleanup, refactoring
  adding missing when, for mapThen / invokeThen
  a bit of cleanup on the relation
sql specific adapter, basic migration config