…dd a new CLD.detect_language_summary.

Also updated FFI to 1.9.18 & RSpec to 3.7.0.

  - CLD.detect_language (returns a Hash)
  - CLD.detect (returns a ResultValue)
  - CLD.detect_language_with_summary (returns a Hash)
  - CLD.detect_with_summary (returns a ResultValue)
  - CLD.Encoding (an enum)
  - CLD.Language (an enum)
  - CLD.language_from_name (takes "English" or "en" and returns CLD.Language[:ENGLISH])

Add language_id (int) to all the structs. We'll be removing code and name
from all structs in the future. Instead, they can be generated on the fly.

…esult memory copying and

freeing is done automatically via factory API: CLD.detect_summary.

Also reworked FFI structs to not pass code & names.  Instead, we'll now use the exposed C APIs to
translate internal Language type (ENUM) to proper the code & name.

Primary public APIs:
  - CLD.detect_language (returns a Hash)
  - CLD.detect (returns a private Result)
  - CLD.detect_language_summary (returns a Hash)
  - CLD.detect_summary (returns a private Summary)

…flect the new APIs.