Extract ELAs from Christian's Shapefile. Assumes ELA to be the last
field on record. Not very stable against slightly different
constructed files
Scatterplot two sets of ELAs with errorbars.

Assumes input files to contain two columns of data. 1st column glacier
IDs, second column ELA values. Errorbars are generated from multiple
occurences of the same ID, so files can be constructed by
concatenating individual years/...
Changed bmp.nc so numbers in netcdf directly match pixel values in bmp
Bugfix in rasterize
Added support for reading glacier areas from 3rd column in x-axis file
added support for extracting glacier areas and dumping them into the
3rd column. Fields are now accessed by their name. Strangely the
records have a bonus field at the start so indexing is a bit strange...