testcase for virtual properties of buffers
make room for more hobject bits in heaphdr; bit allocation is now tight and 4 bits are available for hobject
first draft of buffer virtual length/index property implementation, not as trivial as seems because buffer bytes are the first writable virtual properties
update buffer virtual prop test
guide update on buffer virtual properties
buffer guide improvements
remove some unprintable chars
improve buffer virtual properties test case
add buffer write fast path for plain buffer values; refactor some array index / fast path helpers
guide performance notes re: plain buffer vs. buffer Object
reuse same helper for arr_idx handling in one more place
Merge branch 'buffer-virtual-properties'
releases update