Document concatenating Seq objects with sum in Tutorial

See discussion on https://github.com/biopython/biopython/pull/277
and user query http://www.biostars.org/p/92665/
Update for TogoWS convert - don't use urlencode & data= prefix anymore
Adding http://eutils.ncbi.nlm.nih.gov/eutils/dtd/20060628/esearch.dtd

Reported missing in GitHub issue #287
Entrez DTD http://eutils.ncbi.nlm.nih.gov/eutils/dtd/20060131/esummary-v1.dtd

Reported missing on issue #290
Python 3 fix for MUSCLE subprocess example, issue #284