New features and bug fix

• Added id as arguments to data.labels.format callback. #190
• Added data.color API #177
• Added padding.top and padding.bottom #193
• Modify element structure for region to wrap rect by g #194
• Fixed data.name API #150
• Fixed legend positioning #176
• Fixed axis.min and axis.max to accept the value for x axis #202
• Fixed bug when only 1 data on categorized axis #194
• Fixed anti aliasing on half pixel (but not enough..) #204