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

docs/own-main.md

@@ -16,8 +16,7 @@ If you just need to have code that executes before and/ or after Catch this is t
 #define CATCH_CONFIG_RUNNER
 #include "catch.hpp"
 
-int main( int argc, char* argv[] )
-{
+int main( int argc, char* argv[] ) {
   // global setup...
 
   int result = Catch::Session().run( argc, argv );
@@ -42,7 +41,22 @@ int main( int argc, char* argv[] )
 
   // writing to session.configData() here sets defaults
   // this is the preferred way to set them
-
+  
+  // Verify that all tests, aliases, etc registered properly
+  const auto& exceptions = getRegistryHub().getStartupExceptionRegistry().getExceptions();
+  if ( !exceptions.empty() ) {
+    // iterate over all exceptions and notify user
+    for ( const auto& ex_ptr : exceptions ) {
+        try {
+            std::rethrow_exception(ex_ptr);
+        } catch (std::exception const& ex) {
+            Catch::cerr() << ex.what();
+        }
+    }
+    // Indicate that an error occured before main
+    return 1;
+  }
+  
   int returnCode = session.applyCommandLine( argc, argv );
   if( returnCode != 0 ) // Indicates a command line error
   	return returnCode;