Work around SSL compression methods memory leak in ASIO

Call SSL_COMP_free_compression_methods() because ASIO itself doesn't, even
though it should, because it calls SSL_library_init() which allocates memory
for the compression methods.

Closes #67

Release/src/http/client/http_client_winhttp.cpp

@@ -28,6 +28,26 @@
 
 #include "cpprest/details/http_client_impl.h"
 
+// This is a hack to avoid memory leak reports from the debug MSVC CRT for all
+// programs using the library: ASIO calls SSL_library_init() which calls
+// SSL_COMP_get_compression_methods(), which allocates some heap memory and the
+// only way to free it later is to call SSL_COMP_free_compression_methods(),
+// but this function is unaccessible from the application code as OpenSSL is
+// statically linked into the C++ REST SDK DLL. So, just to be nice, call it
+// here ourselves -- even if the real problem is in ASIO (up to v1.60.0).
+#ifndef NDEBUG
+
+#include <openssl/ssl.h>
+static struct ASIO_SSL_memory_leak_suppress
+{
+    ~ASIO_SSL_memory_leak_suppress()
+    {
+        ::SSL_COMP_free_compression_methods();
+    }
+} ASIO_SSL_memory_leak_suppressor;
+
+#endif // NDEBUG
+
 namespace web
 {
 namespace http