Merge pull request #2 from ReidWeb/master

Replace linear backup retention system with granular one
Rename in preparation for OS agnostic capability
Major re-factor - see extended description

Major changes include:
- Config is now read from a separate file, meaning that updating the script is simpler
- There is now a simple check for all required binaries used by the script before the backup process begins
- SSH authentication is now tested before the backup begins
- write permission is now checked remotely before the backup begins
New OS agnostic script renders this redundant
adjusted bash path to more common linux one

The first line is now the only line that needs to be edited to run successfully on FreeBSD
Added back the granular retention changes
Merged back the granular backup changes
EXPERIMENTAL: switched remote backups to granular system