Add joypad images (#156)

<!--- Provide a general summary of your changes in the Title above -->

## Description
<!--- Describe your changes in detail -->
Taken from https://github.com/n64brew/N64brew-GameJam2024-Template/
(MIT)
Also improves the assets by adding them into sub-directories.

## Motivation and Context
<!--- What does this sample do? What problem does it solve? -->
<!--- If it fixes/closes/resolves an open issue, please link to the
issue here -->
Will allow use in the menu to improve navigation/context.

## How Has This Been Tested?
<!-- (if applicable) -->
<!--- Please describe in detail how you tested your sample/changes. -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->

## Screenshots
<!-- (if appropriate): -->

## Types of changes
<!--- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] Improvement (non-breaking change that adds a new feature)
- [ ] Bug fix (fixes an issue)
- [ ] Breaking change (breaking change)
- [ ] Documentation Improvement
- [x] Config and build (change in the configuration and build system,
has no impact on code or features)

## Checklist:
<!--- Go over all the following points, and put an `x` in all the boxes
that apply. -->
<!--- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
- [ ] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [ ] I have added tests to cover my changes.
- [ ] All new and existing tests passed.

<!--- It would be nice if you could sign off your contribution by
replacing the name with your GitHub user name and GitHub email contact.
-->
Signed-off-by: GITHUB_USER <GITHUB_USER_EMAIL>

.gitignore

@@ -8,6 +8,7 @@
 # Ignore generated files in the libdragon FS
 /filesystem/FiraMonoBold.font64
 /filesystem/*.wav64
+/filesystem/*.sprite
 
 # Ignore external development tools
 /tools/*

Makefile

@@ -85,6 +85,30 @@ SOUNDS = \
 	error.wav \
 	settings.wav
 
+JOYPAD_IMAGES = \
+	joypad_a.png \
+	joypad_b.png \
+	joypad_c_down.png \
+	joypad_c_left.png \
+	joypad_c_right.png \
+	joypad_c_up.png \
+	joypad_d_down.png \
+	joypad_d_left.png \
+	joypad_d_right.png \
+	joypad_d_up.png \
+	joypad_l.png \
+	joypad_r.png \
+	joypad_start.png \
+	joypad_z.png
+# joypad_j_east.png \
+# joypad_j_north.png \
+# joypad_j_northeast.png \
+# joypad_j_northwest.png \
+# joypad_j_south.png \
+# joypad_j_southeast.png \
+# joypad_j_southwest.png \
+# joypad_j_west.png \
+
 OBJS = $(addprefix $(BUILD_DIR)/, $(addsuffix .o,$(basename $(SRCS))))
 MINIZ_OBJS = $(filter $(BUILD_DIR)/libs/miniz/%.o,$(OBJS))
 SPNG_OBJS = $(filter $(BUILD_DIR)/libs/libspng/%.o,$(OBJS))
@@ -92,7 +116,8 @@ DEPS = $(OBJS:.o=.d)
 
 FILESYSTEM = \
 	$(addprefix $(FILESYSTEM_DIR)/, $(notdir $(FONTS:%.ttf=%.font64))) \
-	$(addprefix $(FILESYSTEM_DIR)/, $(notdir $(SOUNDS:%.wav=%.wav64)))
+	$(addprefix $(FILESYSTEM_DIR)/, $(notdir $(SOUNDS:%.wav=%.wav64))) \
+	$(addprefix $(FILESYSTEM_DIR)/, $(notdir $(JOYPAD_IMAGES:%.png=%.sprite)))
 
 $(MINIZ_OBJS): N64_CFLAGS+=-DMINIZ_NO_TIME -fcompare-debug-second
 $(SPNG_OBJS): N64_CFLAGS+=-isystem $(SOURCE_DIR)/libs/miniz -DSPNG_USE_MINIZ -fcompare-debug-second
@@ -101,14 +126,18 @@ $(FILESYSTEM_DIR)/%.wav64: AUDIOCONV_FLAGS=--wav-compress 1
 
 $(@info $(shell mkdir -p ./$(FILESYSTEM_DIR) &> /dev/null))
 
-$(FILESYSTEM_DIR)/%.font64: $(ASSETS_DIR)/%.ttf
+$(FILESYSTEM_DIR)/%.font64: $(ASSETS_DIR)/fonts/%.ttf
 	@echo "    [FONT] $@"
 	@$(N64_MKFONT) $(MKFONT_FLAGS) -o $(FILESYSTEM_DIR) "$<"
 
-$(FILESYSTEM_DIR)/%.wav64: $(ASSETS_DIR)/%.wav
+$(FILESYSTEM_DIR)/%.wav64: $(ASSETS_DIR)/sounds/%.wav
 	@echo "    [AUDIO] $@"
 	@$(N64_AUDIOCONV) $(AUDIOCONV_FLAGS) -o $(FILESYSTEM_DIR) "$<"
 
+$(FILESYSTEM_DIR)/%.sprite: $(ASSETS_DIR)/images/joypad/%.png
+	@echo "    [SPRITE] $@"
+	@$(N64_MKSPRITE) $(MKSPRITE_FLAGS) -o $(dir $@) "$<"
+
 $(BUILD_DIR)/$(PROJECT_NAME).dfs: $(FILESYSTEM)
 
 $(BUILD_DIR)/menu/views/credits.o: .FORCE