Use Ascii armoured output

Note that this doesn't hugely matter. PWman has no trouble reading the
file under normal encryption and will convert it to Ascii when saving it
anyway, but using Ascii up front is more what you'd expect.
Store secure notes in the "launch" field as it's 256 vs 64 char

And secure notes are likely to be longer. Since whole file is encrypted
anyway, doesn't matter which field you use to store things in. Saves
patching PWman to make the password field accept more chars.

Add note to README regarding this known limitation.