Aggregate multiple input data sets

For the image binner `images` (and also for the putative new time histogram tool, see #21), allow the user to pass multiple input events data sets and aggregate them, to increase the signal in the output data. This will require handling the cues and events separately for `--align-trigger`, `--trigger-type`, etc., as well as checks for compatible `--image-size`, etc., and then aggregating the events in the `bincount` step.

从 `images` image-binner 入口点开始，查看关于拟议时间直方图工具的 issue #21。跟踪在 `bincount` 步骤之前如何处理 cues、events、`--align-trigger`、`--trigger-type` 和兼容性选项。完成的标准是：多个输入事件数据集经过验证，在需要时分别处理，并聚合到输出中。

由索引模型根据 Issue 内容生成。