line chart support image

line chart support image

usage:
```
symbol: 'image://{$url}'
```

demo:
```
symbol: 'image://http://echarts.baidu.com/doc/asset/ico/favicon.png'
```

base64 demo:
```
symbol: 'image://data:image/png;base64,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'
```

thx