Davem/xspod

[iabyn]

Rewrite perlxs.pod

This branch completely rewrites and modernises the XS reference manual, perlxs.pod.

The new file is about twice the size of the old one.

This branch:

• deletes some obsolete sections;

• reorders the existing sections into a more logical order;

• adds a large new introductory/overview part, which explains all the background needed to understand what XSUBs do, including SVs, the stack, reference counts, magic etc.

• includes a BNF syntax section

• modernises: e.g. it uses "ANSI" parameter syntax throughout

• has a fully-worked example using T_PTROBJ

Note that although each commit in this branch may have a complex-looking diff for the updating of a particular section, in reality most sections haver been rewritten from scratch, and the diff output is showing paragraph breaks as fixed unchanging points, so that it appears as lots of individual paragraph changes rather than "delete all this text, add new text". If reviewing, it may be easier to just read the final perlxs.pod file instead of looking at the diffs.

• This set of changes requires a perldelta entry, and I will write one later