Support byte mode

[yawn]

• Enable byte mode encoding
• Encrypt w/o armour
• Support in integration test

[yawn]

Even when using base45 encoding and stripping headers + base64 decoding we are above the maximum encoding buffer when dealing with tarsnap keyfiles.

Potential solutions:

• always compress and base45 encode
• add metadata to the file including relative file positions (e.g. 2/6)
• add split (default) and recover (receiving a series of files and combine them) as an alternative

Drawback: that's not "just" age anymore.