Introduce support for building on MinGW/Cygwin systems

All testcases pass!

$ ./basic.exe
Running test (1): two_endpoints
- Time spent during "two_endpoints": 4.003
Running test (2): read_body
- Time spent during "read_body": 0
Running test (3): read_long_body
- Time spent during "read_long_body": 0.999
Running test (4): read_header
- Time spent during "read_header": 1.014
Running test (5): complete
OKOKOKOKOK- Time spent during "complete": 2.991
Running test (6): only_render
OKOKOKOKMethod not AcceptableOK- Time spent during "only_render": 3.002
Running test (7): postprocessor
- Time spent during "postprocessor": 1.001
Running test (8): empty_arg
- Time spent during "empty_arg": 1
** Runner terminated! **
8 tests executed
25 checks
-> 25 successes
-> 0 failures
Total run time: 15.001
Total time spent in tests: 14.01 ms
Average set up time: 0.110111 ms
Average tear down time: 0 ms