Documentation to-do list

[rplzzz]

• Complete list of valid targets for GETDATA messages. I dumped the #defines into Hector Message Targets, but it could use some organization, culling to just those useful to the outside world, etc.
• Complete list of valid targets for SETDATA messages. Same comments as above.
• Complete table of units. I have started one in Hector Units, but it is far from complete
• API Reference. What we have now is kind of a HOWTO, which is a good start, but we should have full call signature and documentation of arguments and return values for all externally-facing methods.
• Clarify time issue - see startDate non-inclusive? #177

(Feel free to add items in-place or strikethrough items that have been completed.)

[bpbond]

These are all either covered elsewhere, or obviated; closing.