Basic yale slicing functions.
Fixed some problems with is_ref?
Yale each with indices iteration for slicing
Almost got yale iteration working with slicing. Added specs. Found bug
in list iteration across slices, which prevents list matrices from being
pretty_printed properly.
Binary search for yale slice iteration, fixed list slice iteration.
Fixed spec problem
Re-factored dense matrix copying
Fixed handling of ndnz and capacity. Adjusted some of the get/ref
routines for slices.
Resolved new yale to yale copy problem
Fixed yale-to-dense slice copy
Fixed yale-to-list slice copying
Clean up debug messages in preparation for merge