Update SimpleWebServer to the latest version(29 Apr, 2019 - d6985ed6)

[withsmilo]

• related issue : [Bug] SIGSEGV occurred in the SimpleWebServer very rarely #551
• Diff between original SimpleWebServer(left) and new SimpleWebServer modified for Clipper(right) is here.

[AmplabJenkins]

Test FAILed.
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Test FAILed.

[AmplabJenkins]

Test PASSed.
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Test PASSed.

[rkooo567]

Thank you for the PR! I appreciate you added [CLIPPER] comment line so that we can easily update the part whenever we update this dependency.

Everything looks good to me, but I have a few questions.

1. Aren't we using C++ formatter anymore? I found some parts of code were formatted in the previous SimpleWebServer V2.1.1.
2. This version (d6985) is literally the newest commit of SimpleWebServer. Do you think it is stable enough? I am afraid we have to keep updating the version because the newest master is unstable. Is it the version your team is currently using?

[rkooo567]

I found in the previous code, these were formatted (I believe we ran the formatter before?). We don't use the C++ formatter anymore? @simon-mo @withsmilo

[withsmilo]

@rkooo567

1. AFAIK, the C++ code formatter is turned off now.
2. We cannot use SimpleWebServer V2.1.1 in the production environment because it has [Bug] SIGSEGV occurred in the SimpleWebServer very rarely #551 issue. Our team is using ver3(21 Sep, 2018 - cfe98038), and will test / update to the latest ver(29 Apr, 2019 - d6985ed6) this week. I think that there will not be a big problem because the changes applied between them are very minor. Please wait for the test result to run for a week.

[rkooo567]

Why don't we add a README.md to record the version/revision hash information? Seems like some C++ dependencies keep track of its version in its directory name, but httpserver does not. I believe it is because we have some additional custom code inside. We can also probably mention whenever we update the version of httpserver, we should remain the parts with // [CLIPPER].

[simon-mo]

Thanks! I'll directly merge this one since test passed already.

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Test PASSed.
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Test PASSed.