Add a Gemspec so we can play nicely with the rest of the RubyGems ecosystem.
user
```ruby
spec = Gem::Specification.new do |s|
  s.name = 'rubyjedi-testunitxml'
  s.version = '0.1.6.3'
  s.authors = ['Henrik Mårtensson', "Laurence A. Lee"]
  s.email = ['dag.henrik.martensson@gmail.com', 'rubyjedi@gmail.com']
  s.homepage = "https://github.com/rubyjedi/testunitxml"
  s.platform = Gem::Platform::RUBY
  s.summary = "testunitxml extends the Test::Unit framework with an assertion for testing well-formed XML documents."
  s.files = Dir['lib/**/*']
end
```
assistant