Add respect to LIB_DIR variable and pkgconfig example

Makefile

@@ -7,7 +7,8 @@
 # Project directories
 SRC_DIR ?= src
 SDK_DIR ?= sdk
-OUT_DIR ?= ./build
+OUT_DIR ?= build
+LIB_DIR ?= lib
 
 # Project definition
 include project.mk
@@ -77,7 +78,7 @@ default: library
 .PHONY:  all dirs clean doc install
 
 install: library
-	cp $(OUT_DIR)/lib$(PROJECT_NAME).so $(PREFIX)/lib64/
+	cp $(OUT_DIR)/lib$(PROJECT_NAME).so $(PREFIX)/$(LIB_DIR)/
 	cp -R include/aisl $(PREFIX)/include/
 
 # vim:ft=make