[Feature] barGap can be applied to single series instead of all series

[BrazilAmando]

What problem does this feature solve?

barGap can be applied to create bullet chart.

However, multiple series bullet chart cannot be create because barGap only work for all series instead of single series. In this issue, FirstVertex wrote a custom function to create multiple series bullet chart.

It's not convinient for daily work. So, is it possible to make barGap to be applied to single series?

What does the proposed API look like?

series: [{
name: '2011年',
type: 'bar',
barWidth: 28,
zlevel: 2,
barGap:'30%',
data: [183, 239, 290, 104, 234, 630]
},
{
name: '2012年',
type: 'bar',
barWidth: 40,
barGap: '-120%',
data: [125, 308, 310, 121, 134, 481]
},
{
name: '2013年',
type: 'bar',
barWidth: 40,
barGap: '40%',
data: [125, 308, 310, 121, 134, 481]
},
{
name: '2014年',
type: 'bar',
barWidth: 40,
barGap: '-120%',
data: [125, 308, 310, 121, 134, 481]
}
]