Add project metadata to the gemspec

As per https://guides.rubygems.org/specification-reference/#metadata,
add metadata to the gemspec file. This'll allow people to more easily
access the source code, raise issues and read the changelog. These
bug_tracker_uri, changelog_uri, documentation_uri, homepage_uri,
source_code_uri, and wiki_uri links will appear on the rubygems page at
https://rubygems.org/gems/webmachine and be available via the Rubygems
API after the next release.

Author: orien

webmachine.gemspec

@@ -15,6 +15,13 @@ Gem::Specification.new do |gem|
   gem.email = ["[email protected]"]
   gem.license = "Apache-2.0"
 
+  gem.metadata["bug_tracker_uri"] = "#{gem.homepage}/issues"
+  gem.metadata["changelog_uri"] = "#{gem.homepage}/blob/HEAD/CHANGELOG.md"
+  gem.metadata["documentation_uri"] = "https://www.rubydoc.info/gems/webmachine/#{gem.version}"
+  gem.metadata["homepage_uri"] = gem.homepage
+  gem.metadata["source_code_uri"] = gem.homepage
+  gem.metadata["wiki_uri"] = "#{gem.homepage}/wiki"
+
   gem.add_runtime_dependency(%q<i18n>, [">= 0.4.0"])
   gem.add_runtime_dependency(%q<multi_json>)
   gem.add_runtime_dependency(%q<as-notifications>, [">= 1.0.2", "< 2.0"])