Making some APIs public.

#get_free_id and #get_free_uid become public.

src/passwd.cr

@@ -115,8 +115,8 @@ class Passwd
 		get_all_groups.map(&.to_csv).join("\n") + "\n"
 	end
 
-	private def get_free_uid
-		uid = 1000
+	def get_free_uid(starting_uid = 1000)
+		uid = starting_uid
 
 		users = get_all_users
 
@@ -127,8 +127,8 @@ class Passwd
 		uid
 	end
 
-	private def get_free_gid
-		gid = 1000
+	def get_free_gid(starting_gid = 1000)
+		gid = starting_gid
 
 		users = get_all_users