Too bad this doesn't help MSVC 2008 build, as explicit operators are
C++11.

The override_features is used to override features that are normally
discretionary features, but in a specific shaper are for various
reasons desired to be bolted on or off, because they've been used
for inherent shaping.  As such, it makes sense that they also
override user features.  Ie. if user turned 'liga' on, we don't
want Khmer shaping to become broken...  Or turn 'clig' off...

Fixes https://github.com/harfbuzz/harfbuzz/issues/1310

Prerequisite for https://github.com/harfbuzz/harfbuzz/issues/1310

Nothing an extra template class wouldn't fix...

Fixes https://github.com/harfbuzz/harfbuzz/issues/1419

Replace @Deprecated ICU API - USCRIPT_CODE_LIMIT

update simple shaping example (closes #298)

add call to `FT_Set_Char_Size`, otherwise default size remains at `0`, and glyph positions come back as `0` too

It is not visually noticeable but apparently affected by kern format2 correct implementation.
I should've checked CoreText result which can't as CircleCI outage.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1421

Optimize harfbuzz big integer conversions

Profiling showed that type conversions were adding considerable cycles in time
spent doing text shaping.

The idea is to optimize it using native processor instructions to help Blink
layout performance.

Doing further investigation revelead that compilers may not use the
proper instruction on ARM 32bits builds (i.e. REV16).

One way to insure that the generated ASM was ideal for both gcc/clang
was using __builtin_bswap16.

Added bonus is that we no longer need to test for CPU architecture.

Use of the deprecated API USCRIPT_CODE_LIMIT prevents harfbuzz
using the ICU4C as a shared library.

The API has been replaced by u_getIntPropertyMaxValue(UCHAR_SCRIPT)

Similar to https://github.com/GoogleChrome/lighthouse/blob/master/.codecov.yml

No strong preference on commenting, feel free to enable it again

Fixes https://github.com/harfbuzz/harfbuzz/issues/1410

Fixes https://github.com/harfbuzz/harfbuzz/pull/1346