Release version 0.0.4

This release contains minor improvements:

• Add lookup_const method to CLocale module and use it [50cb885]
• Document setlocale, strxfrm and strcoll methods [8189e14]
• Fix C compiler warning about wrong % format specifier [5103822]
• Integrate RuboCop and RuboCop RSpec [bbff802]
• Add spec for CLocale module [ca01a61]
• README.md: Add codecov badge [6642cc1]
• Add code coverage using codecov [b26834a]
• Wire up RSpec rake task in Rakefile [28fc4b3]
• travis: Only build pushed branches when a tag is present [18f29a7]
• Add Travis CI badge to README.md [skip ci] [286fb34]
• Add Travis CI config for OS X and Linux [a471d86]
• Add RSpec [0c6348d]
• Add Ruby 2.5 to AppVeyor build matrix [74ba11b]