QOL make our gem requireable and autoload/eager load some constants

[davebenvenuti]

Pairing with @nirvdrum , we noticed require "protoboeuf" didn't work despite having it in our Gemfile which led to some confusion (#170). This makes require "protoboeuf" work and auto- and eagerloads some constants for the user.

• ProtoBoeuf::CodeGen is now autoloaded from the base lib/protoboeuf.rb
• ProtoBoeuf::Google is also now autoloaded from the base lib/protoboeuf.rb
• Everything in lib/protoboeuf/google/**/*.rb is eager loaded when ProtoBoeuf::Google loads. There isn't a clean 1:1 mapping between constants and *.rb files so autoload would be fairly tricky. Although this could be a controversial decision, I think this makes things easier to work with. But feedback is welcome.
• rake well_known_types now generates modules that autoload all child constants for well known types (eg: ProtoBoeuf::Google::Protobuf with the help of ProtoBoeuf::AutoloaderGen!

[rwstauner]

Makes sense, just a few small things to fix

[tenderworks]

I'd prefer we don't do this pattern, and rather generate the requires as part of our .proto to .rb step.

2 reasons:

1. It's important to know what we're requiring
2. I'm not sure if directory listings are sorted (they weren't in the past) and it can cause platform dependent problems.

If generating a file with the requires is to onerous, I can understand and we can go this route, but I'd prefer if we didn't.

[davebenvenuti]

I'll give that a whirl

[davebenvenuti]

Added a new commit: 7dab057

We now generate modules in lib/protoboeuf/google/api.rb and lib/protoboeuf/google/protobuf.rb that autoload all of the constants defined in lib/protoboeuf/google/**/*.rb! Note that they're collapsed by default in the PR diff view because I marked them as autogenerated in .gitattributes. Big thanks to @rwstauner for helping me update the Rakefile in a way where I wouldn't embarrass myself.

https://github.com/Shopify/protoboeuf/blob/7dab057840f374538c061ce438f3b1db5a41f739/lib/protoboeuf/google/api.rb

https://github.com/Shopify/protoboeuf/blob/7dab057840f374538c061ce438f3b1db5a41f739/lib/protoboeuf/google/protobuf.rb