each font definition has it's own respond-to section to override by breakpoint
update example settings
fix getPaddingForHeight function
responsive-font: use map-has-key instead of check agains null
responsive-font: rename line-height-correction-factor to line-height-part
responsive-font: use @extend for font definitions per default
responsive-font: add basic info to README
Merge pull request #9 from astina/better-responsive-font

Better responsive font