public void addFormat(String excelFormatStr, Format format) {
        formats.put(excelFormatStr, format);
    }
Adds a new format to the available formats.
<p>
The value that will be passed to the Format's format method (specified by <code>java.text.Format#format</code>)
will be a double value from a numeric cell. Therefore the code in the format method should expect a
<code>Number</code> value.
</p>

@param excelFormatStr The data format string
@param format         A Format instance
fastexcel-core/src/main/java/cn/idev/excel/metadata/format/DataFormatter.java