Modernise autotools and fix some platform specific stuff

Modernise autoconf
Modernise automake
Properly quote to avoid AC_LANG_SOURCE error
Change version.h to work on platforms which don't have echo -n
Add libpng dependancy
Initial work on second gen spatial filter
Mk II filter image creation compiles and runs, alas still need to do coordinate shift and zero memory before run.
Add coordinate shift to sp filter mkII
Fix two silly mistakes in previous commit or two.
Alter colours to be easier to see
Add gaussian transform to sp mkII and hacks to test it.
Fix signedness bug in Gaussian make and apply.
Add Thresholding to Gaussian.
Reduce precision of Gaussian to reduce compute time.
Make functions names more consistent
First draft of connected components, I know it's not right but will work on it.
Second draft of connected components, still not working but much closer to what it is supposed to be.
working connected components algorithm, still got all the debug code in
Drop chung for now
Tidy up sp filter II labelling

Tidy up sp filter II's labelling so that next_label is held within the data structure rather than outside.
Fix version.h includes

Fix version.h includes to shared/version.h to avoid accidentally picking up version.h from other packages.
sp filt mk II - clean up and optimise cc4

Clean up dead code.
Optimise connected components 4's union find to remember grand-parents as parents.
sp_filt_mkII: measure connected components

Add code to measure connected components in shape.
sp_filt_mkII: draft filter
sp_filt_mkII: clean up code

Clean up functions names and make static.