re2 is built with rebar and we do expect rebar to be in the search PATH.
If rebar can not be found in the search PATH, it will be
automatically downloaded to support/rebar for local usage.

make
or
rebar compile eunit

re2 dependency is automatically downloaded to c_src/re2 by the build script.
Unless otherwise noted, the re2 source files are distributed under the
BSD-style license found in c_src/re2/LICENSE.