Add function to format any dataset following RecruitNet structure

[Pakillo]

so people can use their own data
fixing column names as in RecruitNet database

[jmalcan]

I'm trying to preprare such function, but I'm not convinced now. I think that it would take less time for users to change the 5 column names in their csv files than learning and using any function where they will have to type the names of their variables anyways. Alternatively, we can:
(1) explain at the very beginning of R help files, that the analyses conducted by this package require two datasets, which can be RecruitNet.csv and CanopyCover.cvs or two similar files supplied by the user: one with the interactions data, containing, at least, columns with the names "Study_site", "Plot", "Canopy", "Recruit" and "Frequency", and another with cover data with, at least, the columns "Study_site", "Plot", "Canopy", "Cover" and "Sampled_distance_or_area". The meaning of the variables and internal structure of these files woud also be explained.
(2) add checks in the visible functions to ensure that the required column names occur in the user's data sets. For example:
if ("Study_site" %in% names(int_data) == FALSE) warning("ERROR: your interactions data lacks a column named: Study_site")