TTML2 features for inclusion in IMSC2

Editor's list of TTML2 features intended for inclusion in IMSC2 (albeit perhaps in a constrained fashion).

All IMSC1 features (including IMSC 1.0.1 features) are intended to be supported by IMSC2.

Also see 218

Japanese Script

fontShear

https://www.w3.org/TR/ttml2/#style-attribute-fontShear

ruby

https://www.w3.org/TR/ttml2/#style-attribute-ruby

rubyAlign

https://www.w3.org/TR/ttml2/#style-attribute-rubyAlign

rubyOverflow

https://www.w3.org/TR/ttml2/#style-attribute-rubyOverflow

rubyOverhang

https://www.w3.org/TR/ttml2/#style-attribute-rubyOverhang

rubyPosition

https://www.w3.org/TR/ttml2/#style-attribute-rubyPosition

rubyReserve

https://www.w3.org/TR/ttml2/#style-attribute-rubyReserve

textEmphasis

https://www.w3.org/TR/ttml2/#style-attribute-textEmphasis

textOrientation

https://www.w3.org/TR/ttml2/#style-attribute-textOrientation

fontKerning

https://www.w3.org/TR/ttml2/#style-attribute-fontKerning

textCombine

https://www.w3.org/TR/ttml2/#style-attribute-textCombine

Stereoscopic

disparity

https://www.w3.org/TR/ttml2/#style-attribute-disparity

Text Styling

textShadow

https://www.w3.org/TR/ttml2/#style-attribute-textShadow

Alternate position specification

https://www.w3.org/TR/ttml2/#style-attribute-position

Miscellaneous

Redefine initial values

https://www.w3.org/TR/ttml2/#styling-vocabulary-initial

HDR

tts:luminanceGain