Adds support for Basic Auth in HTTP Endpoint URLs (#884)

lib/postal/http.rb

@@ -18,8 +18,8 @@ module Postal
       request = method.new(uri.path.length == 0 ? "/" : uri.path)
       options[:headers].each { |k,v| request.add_field k, v }
 
-      if options[:username]
+      if options[:username] || uri.user
-        request.basic_auth(options[:username], options[:password])
+        request.basic_auth(options[:username] || uri.user, options[:password] || uri.password)
       end
 
       if options[:params].is_a?(Hash)