support cost option for bcrypt

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Add open method to be able to immediately close a trocla store after using it
 * Add typesafe charset
+* Support cost option for bcrypt
 
 ## to 0.2.3
 

README.md

@@ -168,6 +168,11 @@ options to work properly. These are documented here:
 Password hashes for PostgreSQL servers. Requires the option `username` to be set
 to the username to which the password will be assigned.
 
+### bcrypt
+
+You are able to tune the [cost factor of bcrypt](https://github.com/codahale/bcrypt-ruby#cost-factors) by passing the option `cost`.
+Note: ruby bcrypt does not support a [cost > 31](https://github.com/codahale/bcrypt-ruby/blob/master/lib/bcrypt/password.rb#L45).
+
 ### x509
 
 This format takes a set of additional options. Required are:

lib/trocla/formats/bcrypt.rb

@@ -1,6 +1,7 @@
 class Trocla::Formats::Bcrypt < Trocla::Formats::Base
+  expensive true
   require 'bcrypt'
   def format(plain_password,options={})
-    BCrypt::Password.create(plain_password).to_s
+    BCrypt::Password.create(plain_password, :cost => options['cost']||BCrypt::Engine.cost).to_s
   end
 end