Clara cleanups

* Clara is now split between a header and a cpp file.
* Removed the deprecated `+` and `+=` operators for composing
  a parser.
* Renamed `clara` and `detail` namespaces to be inline with the
rest of Catch2 (they are now `Clara` and `Detail` respectively).
* Taken most of user-exposed types out of the `Detail` namespace
completely (instead of using `using` directives to bring them into
the outer namespace).

src/CMakeLists.txt

@@ -44,7 +44,6 @@ set(INTERNAL_HEADERS
     ${SOURCES_DIR}/catch_assertion_result.hpp
     ${SOURCES_DIR}/internal/catch_test_macro_impl.hpp
     ${SOURCES_DIR}/internal/catch_clara.hpp
-    ${SOURCES_DIR}/internal/catch_clara_upstream.hpp
     ${SOURCES_DIR}/internal/catch_commandline.hpp
     ${SOURCES_DIR}/internal/catch_common.hpp
     ${SOURCES_DIR}/internal/catch_compiler_capabilities.hpp
@@ -138,6 +137,7 @@ set(IMPL_SOURCES
     ${SOURCES_DIR}/internal/catch_assertion_handler.cpp
     ${SOURCES_DIR}/catch_assertion_result.cpp
     ${SOURCES_DIR}/matchers/internal/catch_matchers_combined_tu.cpp
+    ${SOURCES_DIR}/internal/catch_clara.cpp
     ${SOURCES_DIR}/internal/catch_commandline.cpp
     ${SOURCES_DIR}/internal/catch_common.cpp
     ${SOURCES_DIR}/catch_config.cpp

src/catch2/catch_all.hpp

@@ -40,7 +40,6 @@
 #include <catch2/interfaces/catch_interfaces_all.hpp>
 #include <catch2/internal/catch_assertion_handler.hpp>
 #include <catch2/internal/catch_clara.hpp>
-#include <catch2/internal/catch_clara_upstream.hpp>
 #include <catch2/internal/catch_commandline.hpp>
 #include <catch2/internal/catch_common.hpp>
 #include <catch2/internal/catch_compiler_capabilities.hpp>

src/catch2/catch_session.cpp

@@ -176,7 +176,7 @@ namespace Catch {
         if( m_startupExceptions )
             return 1;
 
-        auto result = m_cli.parse( clara::Args( argc, argv ) );
+        auto result = m_cli.parse( Clara::Args( argc, argv ) );
         if( !result ) {
             config();
             getCurrentMutableContext().setConfig(m_config.get());
@@ -239,10 +239,10 @@ namespace Catch {
         return exitCode;
     }
 
-    clara::Parser const& Session::cli() const {
+    Clara::Parser const& Session::cli() const {
         return m_cli;
     }
-    void Session::cli( clara::Parser const& newParser ) {
+    void Session::cli( Clara::Parser const& newParser ) {
         m_cli = newParser;
     }
     ConfigData& Session::configData() {

src/catch2/catch_session.hpp

@@ -42,14 +42,14 @@ namespace Catch {
 
         int run();
 
-        clara::Parser const& cli() const;
-        void cli( clara::Parser const& newParser );
+        Clara::Parser const& cli() const;
+        void cli( Clara::Parser const& newParser );
         ConfigData& configData();
         Config& config();
     private:
         int runInternal();
 
-        clara::Parser m_cli;
+        Clara::Parser m_cli;
         ConfigData m_configData;
         Detail::unique_ptr<Config> m_config;
         bool m_startupExceptions = false;