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, 18 insertions, 0 deletions

diff --git a/src/player/privinc/human_player_private.h b/src/player/privinc/human_player_private.h
new file mode 100644
index 0000000..5d8a557
--- /dev/null
+++ b/src/player/privinc/human_player_private.h
@@ -0,0 +1,18 @@
+#ifndef HUMAN_PLAYER_PRIVATE_H
+#define HUMAN_PLAYER_PRIVATE_H
+
+#include <human_player.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+void human_player_gui_update(struct human_player *h);
+int human_player_gui_render(const struct human_player *h);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* HUMAN_PLAYER_PRIVATE_H */