Redirect directory path prefix to '/usr/local' (#6)

Avoid installing in /usr/ : This is not correct for some machines (MacOS for instance).

Makefile

@@ -28,7 +28,7 @@ sonar: release
 	cppcheck --xml-version=2 --enable=all --std=c++11 src include 2> cppcheck_report.xml
 	/opt/sonar-runner/bin/sonar-runner
 
-prefix = /usr
+prefix = /usr/local
 bindir = $(prefix)/bin
 mandir = $(prefix)/share/man
 
@@ -38,7 +38,7 @@ install: release_debug
 	@ echo ""
 	install budget.man $(mandir)/man3/budget.3
 	install release_debug/bin/budget $(bindir)/budget
-	install completions/bash $(prefix)/../etc/bash_completion.d/budget
+	install completions/bash $(prefix)/etc/bash_completion.d/budget
 	install completions/zsh $(prefix)/share/zsh/site-functions/_budget
 
 clean: base_clean