chore(autocomplete): Add autocomplete exports to the index.ts.

[emoralesb05]

Using the latest nightly build in https://github.com/angular/material2-builds there wasnt a way to import only the MdAutocompleteModule nor its components from @angular/material because it wasnt in the index.ts file.

Looked at the opened PR's and didnt see it in them either, so just creating this PR just in case (Also a nice way to do my first little contribution 😄)

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[emoralesb05]

I signed it!

[googlebot]

CLAs look good, thanks!

[kara]

LGTM. Thanks!

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