Add zero-argument overload for Apply().
Add zero-argument overload for Apply().

Fixes #98.

Change-Id: If67db9730a80c36633fb739c86e058a8c8f92ce0
Reviewed-on: https://code-review.googlesource.com/4960
Reviewed-by: Paul Wankadia <62d4e38bb1380f055ec4b899baa75e52af09c5f7@google.com>

google/re2,google/re2,google/re2,google/re2,google/re2