Add support for multiple parallel reporters

This requires a bunch of different changes across the reporter
subsystem.

* We need to handle multiple reporters and their differing
  preferences in `ListeningReporter`, e.g. what to do when
  we mix reporters that capture and don't capture stdout.
* We need to change how the reporter is given output and
  how we parse reporter's output destination from CLI.
* Approval tests need to handle multireporter option

src/catch2/interfaces/catch_interfaces_config.hpp

@@ -61,7 +61,7 @@ namespace Catch {
         virtual ~IConfig();
 
         virtual bool allowThrows() const = 0;
-        virtual std::ostream& stream() const = 0;
+        virtual std::ostream& defaultStream() const = 0;
         virtual StringRef name() const = 0;
         virtual bool includeSuccessfulResults() const = 0;
         virtual bool shouldDebugBreak() const = 0;

src/catch2/interfaces/catch_interfaces_reporter.cpp

@@ -20,9 +20,6 @@
 
 namespace Catch {
 
-    ReporterConfig::ReporterConfig( IConfig const* _fullConfig )
-    :   m_stream( &_fullConfig->stream() ), m_fullConfig( _fullConfig ) {}
-
     ReporterConfig::ReporterConfig( IConfig const* _fullConfig, std::ostream& _stream )
     :   m_stream( &_stream ), m_fullConfig( _fullConfig ) {}
 

src/catch2/interfaces/catch_interfaces_reporter.hpp

@@ -32,8 +32,6 @@ namespace Catch {
     struct IConfig;
 
     struct ReporterConfig {
-        explicit ReporterConfig( IConfig const* _fullConfig );
-
         ReporterConfig( IConfig const* _fullConfig, std::ostream& _stream );
 
         std::ostream& stream() const;

src/catch2/interfaces/catch_interfaces_reporter_registry.hpp

@@ -23,13 +23,14 @@ namespace Catch {
     using IStreamingReporterPtr = Detail::unique_ptr<IStreamingReporter>;
     struct IReporterFactory;
     using IReporterFactoryPtr = Detail::unique_ptr<IReporterFactory>;
+    struct ReporterConfig;
 
     struct IReporterRegistry {
         using FactoryMap = std::map<std::string, IReporterFactoryPtr, Detail::CaseInsensitiveLess>;
         using Listeners = std::vector<IReporterFactoryPtr>;
 
         virtual ~IReporterRegistry(); // = default
-        virtual IStreamingReporterPtr create( std::string const& name, IConfig const* config ) const = 0;
+        virtual IStreamingReporterPtr create( std::string const& name, ReporterConfig const& config ) const = 0;
         virtual FactoryMap const& getFactories() const = 0;
         virtual Listeners const& getListeners() const = 0;
     };