Eclcompress can use too much memory

It has been observed in logs that `eclcompress` can be killed due to an out-of-memory situation. In a particular case, eclcompress was run on a "xxxx.grid" file of 2.1 Gb, and when it was killed, it consumed 32Gb of memory.

This is unfortunate, and a solution could be for eclcompress to read one keyword at a time, it probably keeps everything for a file in memory at once.