merge pixmap handling from sampler, material.h and ccdemos's image module to new Pixmap class add check for PNG library, allow writing PNG file from a Pixmap simplify demos using new methods from Sampler and Pixmap

Import('env lib')
myenv = env.Clone()
myenv.Append(CPPPATH = ['.','#include'], LIBPATH='#build/lib')
myenv.Prepend(LIBS=['pyrit'])

l = []
l.append( myenv.Program(['vector.cc']) )

myenv.Alias('tests', l)