Support conversion of text color in docx ?

[pchelle]

Thanks to the pandoc raw_attribute, we can currently support the conversion of md documents that include html tags into docx

Another potential tag to convert can be font color:
In md and html, we have usually

<font color="blue">this is blue text</font>

In openxml, it needs to be converted this way:

<w:r><w:rPr><w:color w:val="blue"/></w:rPr>this is blue text</w:r>