Add a matcher that checks exception's message

Only works for exceptions that publicly derive from `std::exception`
and the matching is done exactly, including case and whitespace.

Closes #1649
Closes #1728

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include/internal/catch_capture_matchers.h

@@ -10,6 +10,7 @@
 
 #include "catch_capture.hpp"
 #include "catch_matchers.h"
+#include "catch_matchers_exception.hpp"
 #include "catch_matchers_floating.h"
 #include "catch_matchers_generic.hpp"
 #include "catch_matchers_string.h"

include/internal/catch_matchers_exception.cpp

@@ -0,0 +1,30 @@
+/*
+ *  Created by Martin Hořeňovský on 13/10/2019.
+ *
+ * Distributed under the Boost Software License, Version 1.0. (See accompanying
+ * file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#include "catch_matchers_exception.hpp"
+
+
+namespace Catch {
+namespace Matchers {
+namespace Exception {
+
+bool ExceptionMessageMatcher::match(std::exception const& ex) const {
+    return ex.what() == m_message;
+}
+
+std::string ExceptionMessageMatcher::describe() const {
+    return "exception message matches \"" + m_message + "\"";
+}
+
+}
+Exception::ExceptionMessageMatcher Message(std::string const& message) {
+    return Exception::ExceptionMessageMatcher(message);
+}
+
+// namespace Exception
+} // namespace Matchers
+} // namespace Catch

include/internal/catch_matchers_exception.hpp

@@ -0,0 +1,39 @@
+/*
+ *  Created by Martin Hořeňovský on 13/10/2019.
+ *
+ * Distributed under the Boost Software License, Version 1.0. (See accompanying
+ * file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+#ifndef TWOBLUECUBES_CATCH_MATCHERS_EXCEPTION_HPP_INCLUDED
+#define TWOBLUECUBES_CATCH_MATCHERS_EXCEPTION_HPP_INCLUDED
+
+#include "catch_matchers.h"
+
+#include <functional>
+#include <string>
+
+namespace Catch {
+namespace Matchers {
+namespace Exception {
+
+class ExceptionMessageMatcher : public MatcherBase<std::exception> {
+    std::string m_message;
+public:
+
+    ExceptionMessageMatcher(std::string const& message):
+        m_message(message)
+    {}
+
+    bool match(std::exception const& ex) const override;
+
+    std::string describe() const override;
+};
+
+} // namespace Exception
+
+Exception::ExceptionMessageMatcher Message(std::string const& message);
+
+} // namespace Matchers
+} // namespace Catch
+
+#endif // TWOBLUECUBES_CATCH_MATCHERS_EXCEPTION_HPP_INCLUDED