Build into dist/, list primes to 1,000,000 with timing, add wiki

Makefile

@@ -1,36 +1,39 @@
-# Builds prime_avx2 on Linux (gcc) and Windows (MinGW-w64 / MSYS2 gcc).
+# Builds prime_avx2 into dist/ on Linux (gcc) and Windows (MinGW-w64 / MSYS2 gcc).
 #   make          build
 #   make run      build and run
-#   make clean    remove build output
+#   make clean    remove dist/
 
 CC      ?= gcc
 CFLAGS  ?= -O3 -mavx2 -Wall -Wextra
 LDLIBS  += -lm
 
+DIST    := dist
+
 ifeq ($(OS),Windows_NT)
   EXE   := .exe
-  RM    := del /Q /F
   # make on Windows may use cmd.exe, which needs backslashes
-  RUN   := .\prime_avx2$(EXE)
-  RMTARGET := prime_avx2$(EXE)
+  RUN   := $(DIST)\prime_avx2$(EXE)
+  RMDIR := if exist $(DIST) rmdir /S /Q $(DIST)
 else
   EXE   :=
-  RM    := rm -f
-  RUN   := ./prime_avx2
-  RMTARGET := prime_avx2
+  RUN   := ./$(DIST)/prime_avx2
+  RMDIR := rm -rf $(DIST)
 endif
 
-TARGET := prime_avx2$(EXE)
+TARGET := $(DIST)/prime_avx2$(EXE)
 
 .PHONY: all run clean
 
 all: $(TARGET)
 
-$(TARGET): prime_avx2.c
+$(TARGET): src/prime_avx2.c | $(DIST)
 	$(CC) $(CFLAGS) $< -o $@ $(LDLIBS)
 
+$(DIST):
+	mkdir $(DIST)
+
 run: $(TARGET)
 	$(RUN)
 
 clean:
-	-$(RM) $(RMTARGET)
+	-$(RMDIR)