Add cld2-sys/prepackage.sh which cuts cld2 to fit within 10MB.

- `docs/` has been removed, we don't use them!
- Unused `internal/*generated*.cc` have been removed.
- Used `internal/*generated*.cc` have been stripped of excess comments,
  which brought lots of entropy and didn't compress well.
Merge branch 'prepackage' of https://github.com/lifthrasiir/rust-cld2

Closes #1.

Contributor agreement taken from address below:
https://github.com/emk/rust-cld2/pull/1#issuecomment-63974082

emk: Would you be willing to agree to this contributor statement I adapted from
the Unlicense website?

  I dedicate any and all copyright interest in my contributions to this
  project to the public domain. I make this dedication for the benefit of
  the public at large and to the detriment of my heirs and successors. I
  intend this dedication to be an overt act of relinquishment in perpetuity
  of all present and future rights to this software under copyright law.

lifthrasiir: Yes. I'm glad to do so :)