Performance improvements due to conditional parsing of IO data depending on selected fields.

On my machine, this gives a ~20% improvement in htop process time use with the default config.

ProcessList.h

@@ -113,6 +113,7 @@ typedef struct ProcessList_ {
    unsigned long long int usedSwap;
    unsigned long long int freeSwap;
 
+   int flags;
    ProcessField* fields;
    ProcessField sortKey;
    int direction;