Improved the db:migrate function in the Rakefile to utilize the Sequel API for running migrations, and to allow downgrading to a specific migration easily

Rakefile

@@ -1,8 +1,14 @@
 require 'bundler/setup'
 
 namespace :db do
-  task :migrate do
-    %x{sequel -m 'db/migrations/' 'sqlite://data/gamedata.db'}
+  desc 'Run migrations'
+  task :migrate, [:version] do |t, args|
+    require "sequel/core"
+    Sequel.extension :migration
+    version = args[:version].to_i if args[:version]
+    Sequel.connect('sqlite://data/gamedata.db') do |db|
+      Sequel::Migrator.run(db, "db/migrations", target: version)
+    end
   end
 end