Don't cast to numpy.array when cleaning up raw data

Else fields with large string cause outrageous memory usage
Formatted with `artistic style`

I used artistic style (the `astyle` command) with the following options:
--style=attach
--indent=spaces=4
--convert-tabs
--pad-oper
--pad-header
--unpad-paren
--align-reference=type
--add-brackets
--indent-col1-comments
--close-templates
--max-code-length=79
--lineend=linux

Hopefully a consisten format will make the code easier to work on.
Fix bug when converting values to code where we accidentally cast the value to str (it is supposed to be an int)
modularize nan value conversion

extract from read_data_objects; make a stand alone function convert_nans; do convert_nans inside of read_model_data_from_csv
BUGFIX: use more general isinstance instead of type
Fix confusing bug where codes were being incorrectly cast to string
Merge branch 'data_munging'

Conflicts:
	crosscat/utils/data_utils.py
Merge https://github.com/genos/crosscat
replace ">>" with "> >"

only exception is cpp_code/src/utils.cpp:388
using ours