Fix up Makefile.

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -22,20 +22,20 @@ VERSION  = v$(V_NUM) - $(V_DATE)
 
 # paths
 PREFIX   = /usr/local
-DATA_DIR = $(PREFIX)/share/games/$(BIN)/# the trailing slash is required for paths in the source
+DATA_DIR = $(PREFIX)/share/$(BIN)/# the trailing slash is required for paths in the source
 
 LIBS    = `sdl2-config --libs` -lSDL2_mixer
 LDFLAGS = $(LIBS)
 
 CPPFLAGS = -DDATA_DIR=\"$(DATA_DIR)\" -DVERSION=\"'$(VERSION)'\"
 
-CXX = g++
+CXX ?= g++
 
 OBJ = $(shell find src -iname '*.cpp' -type f | sed 's/\.cpp$$/.o/')
 
 # debug
 #CXXFLAGS = -ggdb -DDEBUG -std=c++14 -Wall `sdl2-config --cflags` $(CPPFLAGS)
-CXXFLAGS = -O2 -std=c++14 -Wall `sdl2-config --cflags` $(CPPFLAGS)
+CXXFLAGS += $(FLAGS) -std=c++14 -Wall `sdl2-config --cflags` $(CPPFLAGS)
 
 all: options davegnukem
 
@@ -64,9 +64,9 @@ dist: clean
 
 install: 
 	# binary
-	mkdir -p $(DESTDIR)$(PREFIX)/games
-	cp -f $(BIN) $(DESTDIR)$(PREFIX)/games
-	chmod 755 $(DESTDIR)$(PREFIX)/games/$(BIN)
+	mkdir -p $(DESTDIR)$(PREFIX)/bin
+	cp -f $(BIN) $(DESTDIR)$(PREFIX)/bin
+	chmod 755 $(DESTDIR)$(PREFIX)/bin/$(BIN)
 	# data
 	mkdir -p $(DESTDIR)$(DATA_DIR)
 	cp -fR data/* $(DESTDIR)$(DATA_DIR)
@@ -91,9 +91,9 @@ install: 
 	cp -f debian/icons/hicolor/32x32/apps/$(BIN).png $(DESTDIR)$(PREFIX)/share/icons/hicolor/32x32/apps
 	chmod 644 $(DESTDIR)$(PREFIX)/share/icons/hicolor/32x32/apps/$(BIN).png
 	# manual page
-	mkdir -p $(DESTDIR)$(PREFIX)/share/man/man6
-	sed 's/VERSION/$(VERSION)/' < debian/$(BIN).6 > $(DESTDIR)$(PREFIX)/share/man/man6/$(BIN).6
-	chmod 644 $(DESTDIR)$(PREFIX)/share/man/man6/$(BIN).6
+	mkdir -p $(DESTDIR)$(PREFIX)/man/man6
+	sed 's/VERSION/$(VERSION)/' < debian/$(BIN).6 > $(DESTDIR)$(PREFIX)/man/man6/$(BIN).6
+	chmod 644 $(DESTDIR)$(PREFIX)/man/man6/$(BIN).6
 
 uninstall:
 	rm -f $(DESTDIR)$(PREFIX)/games/$(BIN) 
