[doc] Document the new PERL version macros

[atoomic]

We need to document the deprecation of the old macro and announce the new ones
but also suggest to use the compare functions instead

#define PERL_REVISION  	          5
#define PERL_VERSION   	        255
#define PERL_SUBVERSION         255

#define PERL_MAJOR_VERSION	      7
#define PERL_MINOR_VERSION	      0
#define PERL_MICRO_VERSION	      0