charts now look much sharper

To get everything looks sharper, move the main container 0.5 pixels in each direction. It's a known issue on D3 (check http://mbostock.github.io/d3/tutorial/bar-2.html). Half-pixel offsets disable anti-aliasing.

Additionally, some values gets rounded and some elements get sharpened by CSS.

Know bugs:
- grid-lines sometimes have an offset of 1px
- does not work after windows.resize