More uiButton documentation.

docs/uiButton.md

@@ -5,3 +5,35 @@ uiButton is a control which represents a clickable button.
 Windows | Unix | OS X
 -----|-----|-----
 ![Button on Windows](images/uiButton_windows.png)|![Button on Unix](images/uiButton_unix.png)|![Button on OS X](images/uiButton_darwin.png)
+
+uiButton derives from [uiControl](uiControl.md).
+
+# uiNewButton()
+
+```c
+uiButton *uiNewButton(const char *text);
+```
+
+Creates a new uiButton with the specifed text.
+
+# func Text()
+```c
+char *uiButtonText(uiButton *b);
+```
+Returns the text shown on the uiButton. Free the returned string with `uiTextFree()`.
+
+# func SetText()
+```c
+void uiButtonSetText(uiButton *b, const char *text);
+```
+Changes the text shown on the uiButton to the given text string.
+
+# func OnClicked
+```c
+void uiButtonOnClicked(uiButton *b void (*handler)(uiButton *, void *), void *data);
+```
+Sets the function that is called when the user clicks the uiButton. The `data` parameter is passed as the second argument to this function. If a handler was previous assigned, this call replaces the old handler with the given one.
+
+The default handler does nothing.
+
+TODO allow NULL to return to default?