save.sh + wren: Add --no-snapshot option

[codewithmichael]

• Addresses #28 (Control Script / Save - Add option to skip snapshotting)
• Potential merge conflict #29 (Option to disable active data file system)
• Potential merge conflict #31 (wren (control script): Reformat usage table with separate RAM and Swap)

This commit adds a --no-snapshot option to both save.sh and the wren control script (when using wren save).

When the new option is used, snapshot creation is skipped entirely and save.sh doesn't even check to see if snapshot creation is possible. An additional message is printed by save.sh when this option is used — where it would normally say "Creating snapshot..." it instead says "Proceeding without snapshot..."

[codewithmichael]

Note: This is likely to cause a merge conflict with #31.