Fix header C++ compatibility

include/groundvm.h

@@ -115,6 +115,10 @@ typedef struct GroundFunction {
     size_t startLine;
 } GroundFunction;
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 GroundProgram groundCreateProgram();
 void groundAddInstructionToProgram(GroundProgram* program, GroundInstruction instruction);
 GroundValue groundRunProgram(GroundProgram* program);
@@ -126,5 +130,8 @@ GroundArg groundCreateReference(GroundArgType type, char* ref);
 
 GroundValue groundCreateValue(GroundValueType type, ...);
 
+#ifdef __cplusplus
+}
+#endif
 
 #endif