ENH : Draft of RCParmamDict

 This is a class for keeping track of default values.  It is a recursive
dictionary so we get some notion of namespaces.
Merge branch 'rc_params' of https://github.com/tacaswell/NSLS2

* 'rc_params' of https://github.com/tacaswell/NSLS2:
  ENH : Draft of RCParmamDict

Tom's pull request