I have a weakness for the half-plate &mdash the &lsquoadha chai&rsquo in a tiny kulhar, the half-portion of jhalmuri in a minuscule paper packet offered by some Kolkata vendors, the miniature dosa that would be slightly less than half a classic Udupi-sized portion. Sephi Bergerson&rsquos Street Food of India is halfway between a paperback and a coffee-table book, and in this format, his gentle photographs become alluring precisely because he&rsquos offering an indicative, not authoritative, guide to eating out, Indian-style.