Added csv support(score only) by Environment variable.

[t2-kob]

I deleted Branch by mistake, so I will make a pull request again. Sorry!

---

UnixBench outputs benchmark score as console, file, and HTML.

With such an output method, it is difficult to process when comparing the results obtained in multiple environments.
Therefore, I made it possible to output the result to CSV.

And this change does not affect the benchmark score.

---

UnixBench was trying support to change directories via Environment variables, I think.
So I decide to use Environment variable "UB_OUTPUT_CSV".

This option will output csv file to "results" directory.
If benchmark result is named Banana-2018-01-12-01, then csv file name is Banana-2018-01-12-01.csv.

usage:

export UB_OUTPUT_CSV=true
./Run -c 1 -c 2 -c 3 int double

output example:

Concurrency,Arithmetic Test (double),Arithmetic Test (int)
1,504156875.4,493839802.2
2,492484439.5,495202784.3
3,517763703.2,520804801.4

[kdlucas]

Looks good, and I like the simplicity of it.