Add cpp-httplib to oss-fuzz

[omjego]

This PR has changes for integrating cpp-httplib with oss-fuzz.

PR in oss-fuzz: omjego/oss-fuzz#1 (Will be merged after some minor changes in Dockerfile)

Have made following changes after referring to this guide:

1. Add fuzz target to fuzz test server code.
2. Add seed corpus and dictionary to help libFuzz generate meaningful inputs
3. Added new targets (server_fuzzer) in Makefile for easier integration with oss-fuzz
4. Add a standalone server fuzz target runner to reproduce bugs reported by oss-fuzz locally.

Usage:

cd test
make fuzz_test 

or run

make all

TODO:
While generating fuzz target binaries OSS-Fuzz requires you to link all your dependencies statically , I was able to do that with openssl but faced some issues with brotli. zlib was available for dynamic linking. Right now only openssl and zlib support is added for fuzz testing.