other notable changes:
 - add salt to delcodes for extra safety
 - finished Reply.Finalize()
 - rename database tables

Other changes:
 - posts now support multiple attachments

TODO:
 - captcha and API keys need be handled by srv/handlers.go: postHandler()
 - add server configurable limit for number of allowed attachments per
   post

Bug fixes:
 - srv/settings.go: changed ReadConfig() to use a pointer receiver;
   config was previously being read into a copy of the Settings struct
   lol

Posts via cURL with attachments were failing due to misunderstanding
of golang multipart.File types and how they differ from os.*File types.
Attachments are now properly uploaded to a dynamically created post
directories.

NB: Post directory permissions are set to 755

Post deletion would leave behind old attachments; this is no longer the
case.

Makefile now installs dependencies via `go get`.