[tomdionysus]

No function, type or declaration changes: code written against the current release compiles and links unchanged, and the old examples build and run against this branch.

Fixes

• Allocating into a hole between blocks cut the assigned chain short, which could lead realloc to treat a live block as free.
• Splitting a free block whose remainder was smaller than a header wrapped freemem to about 4 GiB.
• Chain inserts could leave stale links on the inserted block.
• Growing with realloc could read past the end of a region, or write a free header over the next block.
• pmalloc_addblock added the running free total to totalmem, so it was wrong after a second region; it also accepted NULL and unusably small regions.
• pmalloc_calloc did not check num * size for overflow, and sizes near 4 GiB wrapped when aligned.
• The suballocation example copied a string into a block one byte too small.

Changes

• Alignment is PMALLOC_ALIGN (compile-time or CMake option), defaulting to the pointer size as before. Headers are padded to it, and invalid values fail to compile.
• pmalloc_sizeof reports the requested size again instead of the rounded size. A block that kept a remainder too small to become a free block reports its whole usable size.
• Regions that touch existing memory are kept PMALLOC_ALIGN bytes apart, so they are never merged and the accounting holds.
• PMALLOC_VERSION macros (0.2.0), extern "C" guards, and a CMake pmalloc::pmalloc package with install rules.

Tests and CI

• Tests are rewritten in C on a vendored Unity 2.7.0: 55 tests, a heap invariant checker and seeded stress runs, with 100% line and branch coverage of pmalloc.c. They pass on macOS and Linux, GCC and Clang, 32-bit and 64-bit, alignments 8 to 64, and under ASan and UBSan.
• CircleCI is replaced by GitHub Actions: a build matrix, a Cortex-M0/M4 cross-compile, coverage gated at 100% and uploaded to Codecov, and CodeQL.

Docs

The README is now a getting-started guide with badges. The API reference moves to docs/API.md, and CHANGELOG.md records this release.

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