Modify swatches export script to include version information.

[sjhcockrell]

It would be useful for the exported android/colors.xml file to have two changes in particular:

• Include a comment containing version information, so that when an Android maintainer updates the colors, we can tell the last time they were updated.
• Change the name of the file from colors.xml to swatches.xml (or something similar.) Our Android project currently has a colors.xml file with older versions, so perhaps having a different file naming convention will help. [1]

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[1] Also, feel free to open an issue on the Meetup Android repo if you think we'd be better served by making the modification on the Android side of things.

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See also: #35, meetup/meetup-android#142

[mlc]

date header thing is addressed in #42; filename is irrelevant as it has to get copied around anyway.