BLD : removed scipy build dep

There is logic in image_handler to fail gracefully if it is
not installed.
RENAME : renamed package from pyLightRafters -> pyRafters
DOC : updated the git-doc
DOC : point travis badge at correct build page
ENH : added option to namedtmpfile to get more than one filename
ENH : added basic version of DAG composure

 - will read in DAG, sort out dependancies and then run graph
 - only works on tools with ImageSourec/ImageSink io
 - runs everything in single process
BLD : add networkx as install dependency

 - hopefully will fix travis
RFCT : moved global out of _proc_subtool in compose.py

 - This is incremental work to make setting up the multi-process
   version
RFCT : moved node/tool iteration into a generator

 - more work to make multi-process easy
CLN : removed un-used imports
ENH : added better error checking to NPFrameSink
API : removed tools.basic.ImageDivide

 - Removed because it's behavior is dependent on the details of it's
inputs.  Both FloorDivideImages and TrueDivideImages are available
which will never do something unexpected
TST : added tests for auto-generated tools in basic
BUG : fixed copy-paste bugs in LTThreshold