Add black point compensation

[natural-harmonia-gropius]

I'm not sure if this is needed/necessary. If the answer is yes, it should be done in tone-mapping, just like what bt.2390 did.

Follow https://www.color.org/WP40-Black_Point_Compensation_2010-07-27.pdf

• bpc is already included in bt2390, so remove bt1886 trick here.
• toe of dynamic make image too dark, remove it.
• L_black of bt1886 and inverse been changed to 1 / 1000.

matrices is for bt2020, add it after tone-mapping. as above bt2390 doesn't need this.

glsl-shader=~~/shaders/hdr-toys/utils/clip_both.glsl
glsl-shader=~~/shaders/hdr-toys/transfer-function/pq_inv.glsl
glsl-shader=~~/shaders/hdr-toys/tone-mapping/dynamic.glsl
+ glsl-shader=~~/shaders/hdr-toys/utils/black_point_compensation.glsl
glsl-shader=~~/shaders/hdr-toys/gamut-mapping/bottosson.glsl
glsl-shader=~~/shaders/hdr-toys/transfer-function/bt1886.glsl

Note:

Update README, if this been merged.

[natural-harmonia-gropius]

dynamic now include black_point_compensation, no need for an independent one.