
Copyright (C) 2022  Terence Kelly

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Changes  2022.05May.01_Avon_5  ->  2022.07Jul.19.1658299753 (Avon 6)

This round of changes was largely motivated by persistent gawk.
Thanks to gawk maintainer Arnold Robbins and Corinna Vinschen for
helpful suggestions and to Nelson Beebe for access to machines for
testing.

00_README:
* add notes on OS configuration and performance
* clarify 8-byte machine word requirement
* urge users to run tests with assertions enabled
* clarify (non-)portability of heap files
* update URLs to pma and pm-gawk publications
* add URLs for official gawk

pma.h: pma_init():
* encourage large sparse heap files
* clarify return value
* clarify rules & recommendations for persistent heap file
* integrity check may be slow

pma.c:
* accommodate older compilers that reject certain legal code (himask)
* modernize printf formats, e.g., "z" for size_t
* change some assertions to ERRs
* allow environment variable to over-ride pma_init verbosity
* enforce stricter alignment for memory mapping of heap file
* relax constraints on size of heap file

Future plans (not promises; subject to change):
* new interface to allow clients to msync heap file
* new verbosity level 4:  TRC ("trace") for many current FYIs
* re-arrange integrity checking
* alternative to get/set root:  return pointer to heap's root pointer
* user manual for persistent gawk (intended as part of gawk, not pma)

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