Export GuiSliderPro and add static to GetTextLines (for shared libs) (#470)

I was having issues using it in conjunction with raylib (in Windows), so added these annotations here.

Let me know if it's okay, thanks for the project, Ray!!

src/raygui.h

@@ -754,6 +754,7 @@ RAYGUIAPI int GuiValueBoxFloat(Rectangle bounds, const char *text, char *textVal
 RAYGUIAPI int GuiTextBox(Rectangle bounds, char *text, int textSize, bool editMode);                   // Text Box control, updates input text
 
 RAYGUIAPI int GuiSlider(Rectangle bounds, const char *textLeft, const char *textRight, float *value, float minValue, float maxValue); // Slider control
+RAYGUIAPI int GuiSliderPro(Rectangle bounds, const char *textLeft, const char *textRight, float *value, float minValue, float maxValue, int sliderWidth); // Slider control with extended parameters
 RAYGUIAPI int GuiSliderBar(Rectangle bounds, const char *textLeft, const char *textRight, float *value, float minValue, float maxValue); // Slider Bar control
 RAYGUIAPI int GuiProgressBar(Rectangle bounds, const char *textLeft, const char *textRight, float *value, float minValue, float maxValue); // Progress Bar control
 RAYGUIAPI int GuiStatusBar(Rectangle bounds, const char *text);                                        // Status Bar control, shows info text
@@ -5003,7 +5004,7 @@ static const char *GetTextIcon(const char *text, int *iconId)
 }
 
 // Get text divided into lines (by line-breaks '\n')
-const char **GetTextLines(const char *text, int *count)
+static const char **GetTextLines(const char *text, int *count)
 {
     #define RAYGUI_MAX_TEXT_LINES   128