Dukweb minimal styling to be closer to duktape.org
Merge branch 'web-repl-styling'

Add minimal styling to Dukweb.js REPL to make it match duktape.org
a bit more closely.
Miscellaneous lightfunc fixes

- Call handling assert
- Test case FIXME removal
16-bit fields and heap pointer compression work

Memory optimization work for very low memory devices (96 to 256kB system RAM).
Overall changes are:

- 16-bit fields for various internal structures to reduce their size
- Heap pointer compression to reduce pointer size to 16 bits

When DUK_OPT_LIGHTFUNC_BUILTINS and the new low memory options are enabled,
Duktape initial heap memory usage is about 23kB (compared to baseline of
about 45kB) on x86.

Unless low memory feature options are enabled, there should be no visible
changes to Duktape behavior.

More detailed changes:

- 16-bit changes for duk_heaphdr: pointer compression, refcount
- 16-bit changes for duk_hstring: hash, blen, and clen can all be 16 bits,
  use 0xFFFF as string byte length limit (call sites ensure this limit is
  never exceeded)
- 16-bit changes for duk_hbuffer, use 0xFFFF as buffer length limit
- 16-bit fields for hobject size (entry part, array part), drop hash part
  since it's not usually needed for extremely low memory environments
- 16-bit changes for duk_hcompiledfunction
- Heap pointer packing for stringtable
- Heap pointer packing for 'strs' built-in strings list (saves around 600
  to 700 bytes but may not be a good tradeoff because call site size will
  increase)

Other changes:

- Heaphdr NULL init fix.  The original macros were broken: the double/single
  linked macro variants were the wrong way around.  Now sets through macro
  to work properly with compressed pointers.

- Rename duk_hbuffer CURR_DATA_PTR -> DATA_PTR to reduce macro length
  (previous name was tediously long)

- Rename buffer "usable_size" to "alloc_size" throughout as they have been
  the same for a while now (they used to differ when buffer had an extra NUL).

- Add memory optimization markers to Duktape.env (pointer compression and
  individual 16-bit field options)

- Rename a few internal fields for clarity: duk_hobject 'p' to 'props',
  heap->st to heap->strtable

- Add a safety check for buffer alloc size (should not be triggered but
  prevents wrapping if call sites don't properly check for sizes)

- Other minor cleanups
Implement ajduk ptr compr, pool size tweaks

Also add more AjsHeap pool sizes for measurements.  The resulting pool
total size is >128kB, but only a small part of it is used.  It's good
to have pool entries with 4-byte increments in the low range so that
actual used sizes can be more easily seen.
Internal low memory documentation updates

- Low memory target suggestions, 96kB RAM target (link to Samsung
  presentation)
- Feature options for 16-bit fields
- Feature options for pointer compression
Makefile: align to 4, whitespace, 16-bit opts
Test cases: 16-bit overflow test case, minor fixes
Matrix compile fixme note
Release note: 16-bit changes
Merge branch 'header-16bit-fields'

Memory optimization work for very low memory devices (96 to 256kB system RAM).
Overall changes are:

- 16-bit fields for various internal structures to reduce their size

- Heap pointer compression to reduce pointer size to 16 bits

- Documentation updates to support these changes, particularly
  low-memory.rst and feature-options.rst

When DUK_OPT_LIGHTFUNC_BUILTINS and the new low memory options are enabled,
Duktape initial heap memory usage is about 23kB (compared to baseline of
about 45kB) on x86.  Unless low memory feature options are enabled, there
should be no visible changes to Duktape behavior.

(See commits for detailed description of what internal changes were made.)
Add missing casts to fix g++ build
Merge branch 'fix-gxx-cast-trivia'
Ditz issue update