Where, or how, can I get a complete history of difficulty? I would like to have a complete list of the historical mining difficulty of bitcoin. Preferably it would be a text list or csv, but a webpage that displays the data in any text format will do. 

I've been searching for several hours over the last couple of days with no progress. I'm quite surprised that this is so hard to find...
You can get it for example on blockchain.info. Call up the Difficulty chart, switch the time-frame to "All Time", then use the link labelled "CSV", to download it.

Note that the difficulty only changes every 2016 blocks, which is re-targeted to be about 14 days, in case you wonder why there are so few data points.