remove META from dist (generated by MakeMaker)
declare minimum perl version

since this module uses our, at least 5.6 is required.  May need to
check if this actually still works on 5.6.  Also removing checks
for perl 5.005, since this dist wouldn't even work there anyway.
add gitignore
add license
add new test to MANIFEST
const-c.inc + const-xs.inc on make realclean
add license