ARPSIO
Add an ARPSIO plugin for reading ARPS dem, grids, etc. The given path should be formatted as follows: /path/filename@parameter with parameter being the key to read in the file since the file contains multiple parameters (including dem). The code is currently in LegacyIO. A possible optimization would be to keep a hash map of pointers in the file (as given to fseek()) so that the position of each already found parameters (as well as the current position) could be saved for faster multiple readings.