NameRecord is not copy-constructible, so should be iterator of
const-reference.

If To is const& then From doesn't need to be &.

Instead of is_cr_convertible.

By removing custom copy constructor.

Functionality kinda superset of std:: counterpart.

Unused.

To block template argument deduction.

The first three based on range-v3.

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

Exposed by:

$ make CPPFLAGS=-O0

It was only used for C++<11 which does not allow default parameters
in function templates.  Looks like we cannot support <11 anyway, so,
start cleaning up.