The first three based on range-v3.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1651

Just sending this to bots to see if all happy, then turn it into macro and
apply everywhere.

Part of https://github.com/harfbuzz/harfbuzz/issues/1651

Should be improved for hb_bytes_t.

Oh well.  Again, who does fully understand what is right???

I don't like the hb_remove_reference() hack, but necessary.

Such that it carries lvalues inside.

Using decltype() instead.

Seprate namespace, cleaner, more clear.

Makes it nicer in pipelines.

inline variables are not C++11, so mark them unused...