Creating a function that we can use to convert px to rem.

This improvement prevent the support of old browsers to REM.
When use font-size or any other property of CSS, you put in value the
*remtopx(rem value)*. The example:

p
   font-size: remtopx(1)
—
p
  font-size: 16px
converting all REM value font-size to *remtopx* function.
Merge pull request #1006 from diegoeis/3.1.0

Convertendo rem para px
Merge pull request #1007 from Wylkon/3.0.2

When exists notification bar, added icon to open notification bar
fix media queries
moving track events doc to right place.
Merge pull request #1008 from deividmarques/3.1.0

fix media queries
Merge pull request #1010 from diegoeis/3.1.0

moving track events doc to right place.
Created breakpoint classes documentation.