Internal documentation for fixed strtab, cleanups
Fixed size stringtable with array chaining
Ajduk strtab, extstr valgrind variant, pool sizes
Avoid interning compiled code in duk cmdline
Release note: strtab with array chaining, reorder
Merge branch 'strtab-fixed-arraychain'

Add an alternate string table algorithm with a fixed size hash table and
separate chaining with arrays.  This eliminates large continuous memory
allocations for the string table structure.  The remaining allocations
(for chains) are small, typically 8 to 64 bytes, and match well with other
small allocations which is convenient for a pool allocator.

The alternate string table is enabled with DUK_OPT_STRTAB_CHAIN and the
top level hash table size is given with DUK_OPT_STRTAB_CHAIN_SIZE.  A good
starting point is -DDUK_OPT_STRTAB_CHAIN_SIZE=128.

As a result of this merge there are two string table algorithms (probing
and chaining), and heap pointer compressed variants of each.  As a future
work item the two algorithms could be merged so that one algorithm could
serve both low memory and other environments well.

Other cleanup may be necessary as separate work items.