Added SOP algorithm to features, added Python bindings section, updated GLM path and added note to clone with --recursive.

- Added expression fitting
- Added Surrey Face Model section
- Slightly restructured build and sample section
- Replaced ICIP with the VISAPP publication
- Replaced license badge with static one

Clarified installation instructions for the header include paths

Added 'header-only' and changed the publication to the ICIP paper.