usual/slab: sanitize object size and align.

Too small values for both would make the code crash,
still allow them but replace with working values.

Noticed-by: Yue Du
heap: heap_destroy() works on NULL argument
cfparser: %include directive

This includes body of other file into current one.

Based on patch by Andrew Dunstan.
mk: refresh libusual2.temo
keccak: Sync with new SHA3 draft.

- Sync SHA3 parameters and regtests with new FIPS202 draft.
- Move regular hash api to 'usual/crypto/sha3' module.
- Drop regular hash api from keccak module, use exteded
  sponge API used in spongeshaker Python module.
socket: getpeercreds cleanups
cxextra/pool: initial size, realloc

make reallow work always properly, although not efficiently.
cxextra: pool improvements
bits: multiply with overflow check
cxalloc: make cx=NULL mean USUAL_ALLOC
Remove use of USUAL_ALLOC
usual.m4: INSTALL - use absolute path
utf8: validator

For sanity-checking UTF8 without decoding.
test_cfparser: allow run from top dir
cxextra: custom alignment for pool
cbtree: disallow double keys
cbtree: allow long keys
make: tags
dox: fix file locations
base: support magic clang macros, cleanups