Switch to storing To addresses as a slice

- Changes on-disk storage format
- Changes JSON API
- To and From values are now parsed/formatted by Go's mail.ParseAddress
  function
- Fixed bug in list-entry-template, was not escaping HTML characters
- Updated tests

swaks-tests/run-tests.sh

@@ -31,7 +31,7 @@ export SWAKS_OPT_to="$to@inbucket.local"
 swaks $* --h-Subject: "Swaks Plain Text" --body text.txt
 
 # Multi-recipient test
-swaks $* --to="$to@inbucket.local,alternate@inbucket.local" --h-Subject: "Swaks Multi-Recipient" \
+swaks $* --to="$to@inbucket.local,Alt User <alternate@inbucket.local>" --h-Subject: "Swaks Multi-Recipient" \
   --body text.txt
 
 # HTML test