Feature/progress (#17)

* improve example gui. Add simple pages

* return old progress bar with example

* base progress with steps, there is bug with step? 1 ~= 1, small delta?

* polish progress, check float error case

* add callback on end of "to" function, value check

* start of green/red in progress

* add first version of rich progress bar

* make green bar darker

* rich bar fixes

* add delay, before filling in rich progress

* PR fixes

* remove dublicate of 'progress_rich'

example/gui.atlas

@@ -4,6 +4,21 @@ images {
 images {
   image: "/example/res/green_long.png"
 }
-margin: 0
-extrude_borders: 0
+images {
+  image: "/example/res/progress_back.png"
+}
+images {
+  image: "/example/res/progress_green.png"
+}
+images {
+  image: "/example/res/progress_red.png"
+}
+images {
+  image: "/example/res/progress_yellow.png"
+}
+images {
+  image: "/example/res/empty.png"
+}
+margin: 2
+extrude_borders: 2
 inner_padding: 0