joinfromvarname not character vector throws an error

[allanjust]

if the variable that is the key in joinfrom is not a character we try to make it one and that doesn't work right now.

Because the key values are being stored in rownames (in makepointmatrix, for use in the knn), we are trying to coerce (unsuccessfully) to character
https://github.com/allanjust/aodlur/blob/master/R/nearestbyday.R#L42