Update font stack.

- Remove DejaVu Sans since it doesn't work with the letter spacing.
- Replace Bitstream Charter with Freesans, a sans-serif alternative.
- Replace Tinos with Arimo, a sans-serif alternative.
update HISTORY.md with new font-stack
Remove "Droid Sans" from the font stack.

Arch Linux supports Arimo so Droid Sans shouldn't be needed.
https://wiki.archlinux.org/index.php/Fonts
Revert "Remove "Droid Sans" from the font stack."

This reverts commit 1a24fa0baa01e48e6a706c1f2e31447020594165.
Looks like Android < 4 only has 3 fonts installed -
* Droid Sans
* Droid Serif
* Droid Sans Mono

So we do need to keep Droid Sans in.
http://www.granneman.com/webdev/coding/css/fonts-and-formatting/default-fonts/#android
Update code comments about Grids font stack.

Closes #41