evangowan/icesheet: ICESHEET 2.0

In this release, there is now a series of scripts to calculate the Antarctic, Eurasian, North American and Patagonia ice sheets, located in the folder "global". Margin reconstructions are provided at 2500 year intervals for the past 80000 years. There are also some changes to the main ICESHEET program that loads the shear stress and topography files to memory, rather than reading from the file on the hard disk. This substantially decreases the amount of time to run the program, often by a factor of five.