Supported properties:
* text-decoration (as shorthand for other text-decoration properties)
* text-decoration-color
* text-decoration-line
* text-decoration-style
* text-decoration-thickness
Changes in the container::create_font:
```litehtml::uint_ptr create_font(const font_description& descr, const document* doc, litehtml::font_metrics* fm);```
All font parameters are moved to the ```font_description``` structure.
* Added subscripts/superscripts baseline shift to the font_metrics
* Improved rendering of inline elements with top and bottom vertical align
* Improved rendering of the line-height property
1. Using container_cairo_pango for running tests.
2. Added Dockerfile to create docker container for building litehtml
tests
3. Added script run_render_tests.sh to build litehtml tests in the
docker container
4. Added render2png target (cmake -DLITEHTML_BUILD_RENDER2PNG). This
utility allow to render html file into a png file.
5. Tests building are off by default.
Use "cmake -DLITEHTML_BUILD_TESTING=ON" command to buid tests
6. Added container_cairo_pango::get_font_options. Overwrite this method
to control fonts rendering.
