More versatile export script

[shippy]

43 implemented a basic export script, which will do for most purposes. Improvements should allow for:

• [ ] concatenating blocks that collect different variables in one file (#89),
• [ ] explicit naming of participants of interest in an argument,
• [ ] concatenating date vectors into the standard datetime format per ISO 8601

[shippy]

• [ ] the taskName argument can also double as dataPath article if tasks/<taskName> does not exist