Initialize module support

go.mod

+module modernc.org/lexer
+
+require (
+	golang.org/x/exp v0.0.0-20181106170214-d68db9428509
+	modernc.org/fileutil v1.0.0
+)

go.sum

+golang.org/x/exp v0.0.0-20181106170214-d68db9428509 h1:k21GX33vzpH/syMF7TgrLxe8ILtvwbyuHtEO3ebR82E=
+golang.org/x/exp v0.0.0-20181106170214-d68db9428509/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
+modernc.org/fileutil v1.0.0 h1:Z1AFLZwl6BO8A5NldQg/xTSjGLetp+1Ubvl4alfGx8w=
+modernc.org/fileutil v1.0.0/go.mod h1:JHsWpkrk/CnVV1H/eGlFf85BEpfkrp56ro8nojIq9Q8=