create `data/summary/{metric}.csv` files

[yegor256]

For each metric, let's make steps/aggregate.sh create data/summary/{metric}.csv files, which will have the following structure (for example, data/summary/LOC.csv):

repository,count,sum,average,mean,min,max
yegor256/cam,28,500,45.3,48.2,1,90
yegor256/cactoos,...
yegor256/takes,...

Here:

• 28 is the number of .m files generated for the repository
• 500 is the summary of all LOC metric values for all files in the yegor256/cam repo
• 45.3 is the arithmetic average
• 48.2 is the mean
• 1 is the smallest value of LOC in the repo
• 90 is the largest value of LOC in the repo

Maybe we can create a new additional step for this sumarization (like steps/summarize.sh)