Remove symbols like '[' and '#' from the headers of the results files

[jfinken]

Our internal query engine cannot handle symbols in the keys (without escaping them) of the headers of the results files. This PR replaces symbols like % with perc etc.

Before

time[ms]   cpu[%]  arena[KB]       in_use[KB]      mmap[KB]        rss[KB]         vsz[KB]         
0          0       0             0                    0              0              0              
1000           1.9       41844          36078          129292         97260          3396848        
...

After

time_ms        cpu_perc  arena_KB       in_use_KB      mmap_KB        rss_KB         vsz_KB         
0              0         0              0              0              0              0              
1000           1.9       41844          36078          129292         97260          3396848        
...

This PR merges to mauro/iron-events-executor for Humble and Iron support. PR-128 merges to master.