replace default values in Makefile with more generic terms. local.conf can override them anyways.

Makefile

@@ -5,8 +5,8 @@ ifeq ($(wildcard local.conf),local.conf)
 endif
 
 PREFIX?=$(HOME)/local/
-BOOST_INCLUDE?=$(HOME)/dev/boost_1_72_0
-BOOST_LIB?=$(HOME)/dev/boost_1_72_0/stage/lib
+BOOST_INCLUDE?=$(PREFIX)/include/
+BOOST_LIB?=$(PREFIX)/lib/
 
 AR?=ar
 CC?=cc