readme: Fix metadata field in the example
Add September's presentation
Makefile: Remove ssh_upload target

This would clobber the permissions if used, so remove it.
Support older rsync versions

Version 3.0.9 (in Ubuntu 12.04) doesn't support the --chmod=D755,F644
syntax: it requires the symbolic notation.  Nor does the version on
Enigma, so change it.
Add Pelican's cache files to gitignore