Fixed issue #17 priv/bcrypt not built with rebar3

rebar.config

@@ -8,10 +8,18 @@
   {"DRV_LDFLAGS","-shared $ERL_LDFLAGS -lpthread"},
   {"darwin", "DRV_LDFLAGS", "-bundle -flat_namespace -undefined suppress $ERL_LDFLAGS -lpthread"},
   {"solaris", "ERL_CFLAGS", "-lnsl $ERL_CFLAGS"},
-  {"DRV_CFLAGS","-Ic_src -Wall -fPIC $ERL_CFLAGS"}
+  {"DRV_CFLAGS","-Ic_src -Wall -fPIC $ERL_CFLAGS"},
+  {"LDFLAGS", "$LDFLAGS -lpthread"}
 ]}.
 
-{port_specs, [{"priv/bcrypt_nif.so", ["c_src/*.c"]}]}.
+{port_specs, [
+    {"priv/bcrypt_nif.so", ["c_src/*.c"]},
+    {"priv/bcrypt", [
+        "c_src/bcrypt_port.c",
+        "c_src/bcrypt.c",
+        "c_src/blowfish.c"
+    ]}
+]}.
 
 %% These post_hooks are for rebar2. rebar.config.script removes them if
 %% rebar3 is detected