Add relx improvements

Add ability to config relx in-line options by setting RELX_OPTS
Fix using RELX_CONFIG variable
Use relx 0.5.0

README.md

@@ -198,6 +198,8 @@ file is fetched.
 `RELX_URL` is the location where `relx` can be downloaded if it is
 not found locally.
 
+`RELX_OPTS` is for setting relx in-line options, if any.
+
 Extra targets
 -------------
 

erlang.mk

@@ -58,7 +58,8 @@ ifneq ($(wildcard $(RELX_CONFIG)),)
 RELX ?= $(CURDIR)/relx
 export RELX
 
-RELX_URL ?= https://github.com/erlware/relx/releases/download/0.4.0/relx
+RELX_URL ?= https://github.com/erlware/relx/releases/download/v0.5.0/relx
+RELX_OPTS ?=
 
 define get_relx
 	wget -O $(RELX) $(RELX_URL) || rm $(RELX)
@@ -66,7 +67,7 @@ define get_relx
 endef
 
 rel: clean-rel all $(RELX)
-	@$(RELX)
+	@$(RELX) -c $(RELX_CONFIG) $(RELX_OPTS)
 
 $(RELX):
 	@$(call get_relx)