Added an option to MemoryProcessors with a possibility to disable formatting.

I  would like to use MemoryProcessors for reporting memory footprint to Logstash. 
Currently, `MemoryProcessor` formats the data as string in flexible format, i.e. you can get 500.10 KB or 100.23 MB in your logs. The problem is, this values cannot be compared, or plotted, etc. Because of this, I've added a construct option to `MemoryProcessor`, which turns the formatting off and you get an integer number as a result.
I've also made a `formatBytes` class non-static, because I don't know, why it should be static, maybe there is a reason behind this?