Bug squashing for remarks and weird LI6400 files

[hrdawson]

Improving the functionality of this very helpful package so that it works more smoothly and with different kinds of LICOR 6400 weirdness.

• Previously, any remark made before data were collected was dropped. That first remark is now imported and assigned to any obs made before the second remark.
• Sometimes the LI6400 generates multiple data headers and starts to the data. Previously, this broke the read.csv function. Now the file will be read in, but with a warning message so that the user knows that it creates a potential one-to-many issue when joining remarks to the data. (Some day I hope to find a way to fix the one-to-many issue as well but I haven't figured it out yet.)