improve documentation for column names

[rBatt]

As an example: ?k.cole says the argument is wind. Need to describe what arguments k.cole() takes when passed a data.frame, as for the data.frame S3 method. Specifically, the header name. But also the format of the datetimes (I think "datetime" is the desired header, as per my interpretation of the $ index at https://github.com/GLEON/LakeMetabolizer/blob/master/R/k.cole.R#L14).

I realize things are in flux, which is why this isn't yet documented. But I think Luke's data.frame/ default methods make sense, and we'll probably use them. Thus, we should start organizing the documentation around this framework.

[rBatt]

Maybe the real point here is that the help files for those functions need to reflect that they can accept either data.frames or just the wnd (e.g.) vector. Right now it's not clear to a user that k.cole() (etc.) has this hugely convenient functionality.

[lawinslow]

I didn't update the documentation yet because I wasn't sure I wanted to keep it. What do you think, is it a mode of operating that we should keep around? If yes, then I'll start working on documentation.

[rBatt]

I've been plugging away at some old metabolism stuff from scratch (pain in the $%@). I'll have a fuller opinion soon. I think your "ts" approach is absolutely essential. That's my current perspective.

[lawinslow]

Ok, that's enough for me. When trying to use it, I also found that some way to handle the diversity of inputs was absolutely essential. Let's go with this for now and see what people think.