Call Python scripts with the virtualenv directory created in
`DOC_DIR/env'. Also ignore the folder in .gitignore.
* builds/freetype.mk (refdoc-venv): Change all calls to local venv.
* docs/reference/.gitignore: Add directory `env/'.
Add required folders, assets and gitignore rules for docwriter. Static
site directory `docs/reference/site/' will be created by MkDocs.
* docs/reference/.gitignore: Ignore HTML, markdown and mkdocs.yml file.
* docs/reference/markdown: New folder to store generated markdown files.
correctly to generate the API reference in 'docs/reference'
* src/tools/docmaker/tohtml.py: update to output nicer fields lists
in the API reference
* src/base/ftobjs.c (FT_Load_Glyph): FT_LOAD_TARGET_LIGHT now
forces auto-hinting
* freetype/freetype.h: updating the documentation for
FT_LOAD_TARGET_XXX and FT_Render_Mode values
