*: Split off headers into their own folder

Main reason is so we don't have that stupid arl prefix directory in
our source code.  Now our source code is flat, and we can still
reference headers by linking from root.

Makefile

@@ -8,7 +8,7 @@ UNITS=main lib/vec lib/sv parser/ast parser/parser
 OBJECTS:=$(patsubst %,$(DIST)/%.o, $(UNITS))
 
 LDFLAGS=
-GFLAGS=-Wall -Wextra -Wpedantic -std=c23 -I./src/
+GFLAGS=-Wall -Wextra -Wpedantic -std=c23 -I./include/
 DFLAGS=-ggdb -fsanitize=address -fsanitize=undefined
 RFLAGS=-O3
 
@@ -26,7 +26,7 @@ DEPDIR=$(DIST)/deps
 $(OUT): $(OBJECTS) | $(DIST)
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
-$(DIST)/%.o: src/arl/%.c | $(DIST) $(DEPDIR)
+$(DIST)/%.o: src/%.c | $(DIST) $(DEPDIR)
 	$(CC) $(CFLAGS) $(DEPFLAGS) $(DEPDIR)/$*.d -c -o $@ $<
 
 $(DIST):