go.talks/pkg/present: read lines with bufio.Scanner
go.talks/pkg/present: read lines with bufio.Scanner

This should handle "\r\n" line endings properly.

Fixes golang/go#5339.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/10483043

Karthikvb/talks,Karthikvb/talks,Karthikvb/talks,Karthikvb/talks,Karthikvb/talks,Karthikvb/talks