Fix Line Chart fill with negtive values.

The base line of line chart fill start from 0 but not bottom of the chart.
Fix bar char negative values.

Fix bar char negative values.
prevent divide by zero error when calculating a circumference
Alignment fix for zero-height columns in bar charts

When drawing a bar chart with zero-height columns, which effectively are
simple lines, they are are drawn slightly lower than non-zero height
columns. Account for this.
Minor typos
Merge branch 'piechart-redraw-after-zero-segment-values' of https://github.com/chasd00/Chart.js
Merge branch 'patch-1' of https://github.com/Winnetou/Chart.js
Merge branch 'master' of https://github.com/pugnascotia/Chart.js
Merge branch 'master' of https://github.com/cadmuxe/Chart.js
Remove unused code