Improved performance of compile_list

Compile list now uses a more reader-friendly version the taxon table (pollen.equiv.RData, also added, with help page) and returns a full pollen object, just like the one returned by get_download.  It's also a bit faster since it doesn't need to pull down data from the API, using only data stored in the pollen object.

This helps resolve #35, by removing the ddply command, but doesn't completely resolve it.