Use (void) for function prototypes with no parameters

This is required when compiling these headers as C code. These were
omitted becuase before the addition of examples these headers were
only compiled locally as C++ files where adding the void keyword is
not needed.

include/SFML/Graphics/RenderStates.h

@@ -50,6 +50,6 @@ typedef struct
 /// \brief Define the default values for a RenderState
 ///
 ////////////////////////////////////////////////////////////
-CSFML_GRAPHICS_API sfRenderStates sfRenderStates_default();
+CSFML_GRAPHICS_API sfRenderStates sfRenderStates_default(void);
 
 #endif // SFML_RENDERSTATES_H

include/SFML/Graphics/RenderTexture.h

@@ -326,7 +326,7 @@ CSFML_GRAPHICS_API const sfTexture* sfRenderTexture_getTexture(const sfRenderTex
 /// \return The maximum anti-aliasing level supported by the system
 ///
 ////////////////////////////////////////////////////////////
-CSFML_GRAPHICS_API unsigned int sfRenderTexture_getMaximumAntialiasingLevel();
+CSFML_GRAPHICS_API unsigned int sfRenderTexture_getMaximumAntialiasingLevel(void);
 
 ////////////////////////////////////////////////////////////
 /// \brief Enable or disable the smooth filter on a render texture

include/SFML/Graphics/Texture.h

@@ -403,7 +403,7 @@ CSFML_GRAPHICS_API void sfTexture_bind(const sfTexture* texture, sfTextureCoordi
 /// \return Maximum size allowed for textures, in pixels
 ///
 ////////////////////////////////////////////////////////////
-CSFML_GRAPHICS_API unsigned int sfTexture_getMaximumSize();
+CSFML_GRAPHICS_API unsigned int sfTexture_getMaximumSize(void);
 
 
 #endif // SFML_TEXTURE_H

include/SFML/Graphics/VertexBuffer.h

@@ -248,7 +248,7 @@ CSFML_GRAPHICS_API void sfVertexBuffer_bind(const sfVertexBuffer* vertexBuffer);
 /// \return True if vertex buffers are supported, false otherwise
 ///
 ////////////////////////////////////////////////////////////
-CSFML_GRAPHICS_API sfBool sfVertexBuffer_isAvailable();
+CSFML_GRAPHICS_API sfBool sfVertexBuffer_isAvailable(void);
 
 
 #endif // SFML_VERTEXBUFFER_H