Rename protobuf Ruby module to google/protobuf and rework its build
system. The Ruby module build now uses an amalgamated distribution of
upb, and successfully builds a Ruby gem called 'google-protobuf' with
module 'google/protobuf'.

ruby/google-protobuf.gemspec

diff --git a/ruby/google-protobuf.gemspec b/ruby/google-protobuf.gemspec
new file mode 100644
index 0000000..87033ac
--- /dev/null
+++ b/ruby/google-protobuf.gemspec
@@ -0,0 +1,22 @@
+class << Gem::Specification
+  def find_c_source(dir)
+    `cd #{dir}; git ls-files "*.c" "*.h" extconf.rb Makefile`.split
+    .map{|f| "#{dir}/#{f}"}
+  end
+end
+
+Gem::Specification.new do |s|
+  s.name        = "google-protobuf"
+  s.version     = "3.0.0.alpha.2"
+  s.licenses    = ["BSD"]
+  s.summary     = "Protocol Buffers"
+  s.description = "Protocol Buffers are Google's data interchange format."
+  s.authors     = ["Protobuf Authors"]
+  s.email       = "protobuf@googlegroups.com"
+  s.require_paths = ["lib"]
+  s.extensions  = ["ext/google/protobuf_c/extconf.rb"]
+  s.files       = ["lib/google/protobuf.rb"] +
+                  # extension C source
+                  find_c_source("ext/google/protobuf_c")
+  s.test_files = `git ls-files -- tests`.split
+end