Collect startup exceptions instead of throwing them

Previously, some errors in Catch configuration would cause exceptions to
be thrown before main was even entered. This leads to call to
`std::terminate`, which is not a particularly nice way of ending the
binary.

Now these exceptions are registered with a global collector and used
once Catch enters main. They can also be optionally ignored, if user
supplies his own main and opts not to check them (or ignored them
intentionally).

Closes #921

include/internal/catch_registry_hub.hpp

@@ -14,6 +14,7 @@
 #include "catch_reporter_registry.hpp"
 #include "catch_exception_translator_registry.hpp"
 #include "catch_tag_alias_registry.h"
+#include "catch_startup_exception_registry.h"
 
 namespace Catch {
 
@@ -39,7 +40,9 @@ namespace Catch {
             virtual ITagAliasRegistry const& getTagAliasRegistry() const override {
                 return m_tagAliasRegistry;
             }
-
+            virtual StartupExceptionRegistry const& getStartupExceptionRegistry() const override {
+                return m_exceptionRegistry;
+            }
 
         public: // IMutableRegistryHub
             virtual void registerReporter( std::string const& name, IReporterFactoryPtr const& factory ) override {
@@ -57,12 +60,16 @@ namespace Catch {
             virtual void registerTagAlias( std::string const& alias, std::string const& tag, SourceLineInfo const& lineInfo ) override {
                 m_tagAliasRegistry.add( alias, tag, lineInfo );
             }
+            virtual void registerStartupException( std::exception_ptr const& exception ) override {
+                m_exceptionRegistry.add(exception);
+            }
 
         private:
             TestRegistry m_testCaseRegistry;
             ReporterRegistry m_reporterRegistry;
             ExceptionTranslatorRegistry m_exceptionTranslatorRegistry;
             TagAliasRegistry m_tagAliasRegistry;
+            StartupExceptionRegistry m_exceptionRegistry;
         };
 
         // Single, global, instance