Remove Inline Output Mode; Automate Inlining in Composer

Closes #9 (closed)

• Remove inline output mode since it no longer makes sense
• Refactor the output_mode configuration option to the header_only boolean flag
• Refactor CMake function interface to take HEADER_ONLY option instead of OUTPUT_MODE argument
• Update composer to automatically generate inline definitions for functions, methods, and kernels, in header-only output mode
• Add a short section on header-only codegen to the docs

tests/generator_scripts/source/ComposerHeaderOnly.harness.cpp

@@ -8,11 +8,23 @@
 int main(void) {
     assert( twice(13) == 26 );
 
-    std::vector< int64_t > arr { 1, 2, 3, 4, 5, 6 };
-    twiceKernel(arr);
+    {
+        std::vector< int64_t > arr { 1, 2, 3, 4, 5, 6 };
+        twiceKernel(arr);
 
-    std::vector< int64_t > expected { 2, 4, 6, 8, 10, 12 };
-    assert ( arr == expected );
+        std::vector< int64_t > expected { 2, 4, 6, 8, 10, 12 };
+        assert ( arr == expected );
+    }
+    
+    {
+        std::vector< int64_t > arr { 1, 2, 3, 4, 5, 6 };
+        ScaleKernel ker { 3 };
+
+        ker( arr );
+
+        std::vector< int64_t > expected { 3, 6, 9, 12, 15, 18 };
+        assert ( arr == expected );
+    }
 
     return 0;
 }