Create NXcanSAS.nxdl.xml

initial commit, templated from NXsas definition
Added common group attributes and some content in SASdata
* all metadata content from 1D SASentry and SASsample groups defined
* TODO items noted
finish initial description of SASdata group
completed SAStransmission_spectrum
completed SASsource
bring it all inside the NXsubentry
add canSAS structure drawings
complete SAScollimation
completed SASdetector
add structure figures to all canSAS groups
completed SASprocess and SASprocessnote
various minor corrections after building manual pages on a linux system
refs #333:

* moved developer tests to separate file
* reorganize to cleaner, callable interface
* same program as before
fixes #333
minor
make sure the figures do not take too much space
resolve TODO items concerning units
Merge pull request #338 from canSAS-org/master

for review at 2014 NeXus Code Camp
we agreed to pull this into the master at the Code Camp today
useful addition, identifies the order of NXprocess groups