Allow Nulls in Mountain Chart
Allow Nulls in Mountain Chart

When filling the line chart we now handle nulls.  Instead of filling to
data[0], we now keep track of the start value to fill to.  When skipping
null values we conditionally fill the previous mountain.  After fill,
the path is reset.

alanponce/Flotr2,HumbleSoftware/Flotr2,beastlike/Flotr2,jessiejea/Flotr2,jessiejea/Flotr2,jessiejea/Flotr2,RobertoMalatesta/Flotr2,beastlike/Flotr2,alanponce/Flotr2,alanponce/Flotr2,RobertoMalatesta/Flotr2,HumbleSoftware/Flotr2,beastlike/Flotr2,nicgallardo/Flotr2,nicgallardo/Flotr2