Calysto-scheme

* set status on error
* Allow (dict) with no args
* (getitem ...) can get attr now; updated docs

* Fixed error for Python3
* Add info on Scheme to Ref Guide
* Ref Guide notebook updates

* fixes for Python2
* fixed python-eval/exec, added to Ref Guide
* WIP: Added notebook from class notes
* Updated a couple of scheme doc-strings
* Fixed unbound module error message
* fixed load-as

* scheme modules in search path
* Added SCHEMEPATH

* added python-eval, python-exec
* added ability to run magics in console

* add vector-length
* import CalystoScheme at top