Revamp gui component

`gui` was tighly coupled to game logic, and could not be extended for
other purposes. Therefore, a generic GUI implementation, loosely
inspired by well-known GUI frameworks such as GTK, is now provided, with
the following properties:

- Does not depend on dynamic or static memory allocation, only automatic
(i.e., stack) memory allocation required.
- Portable among existing implementations.
- Simple to extend.
- Tiny memory footprint.

`gui` is now composed by GUI elements that can be chained to form a tree
structure. This is useful e.g.: to calculate X/Y coordinates for a given
GUI element given its parent(s).

This commit also refactors the older implementation, moving
game-specific logic into `player` and making use of the new component.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/gui/privinc/gui_private.h b/src/gui/privinc/gui_private.h
new file mode 100644
index 0000000..af18dcd
--- /dev/null
+++ b/src/gui/privinc/gui_private.h
@@ -0,0 +1,17 @@
+#ifndef GUI_PRIVATE_H
+#define GUI_PRIVATE_H
+
+#include <gui.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+void gui_coords(const struct gui_common *g, short *x, short *y);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* GUI_PRIVATE_H */