PSR-4 support. Capitalized namespace. Moved helper class to Jyggen\Curl.

Will merge this eventually. This will bump the package to 4.0, no doubt, and break everything everywhere.

#### PSR-4 Support?

It's new and pretty. Won't break anything by itself.

#### Capitalized Namespace?

Because lowercase namespaces are weird. `jyggen\Curl` will turn into `Jyggen\Curl`.

#### Moved helper class?

Yes. `jyggen\Curl` is now `Jyggen\Curl\Curl` to keep everything in the namespace.