Equivalent number values for Pango markup's font sizes

[Tomasz Jankowski <tomcioj gmail com>]

Hello!

I want to change font size for text cell renderer objects in my tree view.
One way is to set strings via "markup" property, but it's inconvenient. What
are number equivalents of Pango markup sizes like "small", "large",
"x-large"? I want to avoid using nonstandard font sizes in my application.