Text encryption

[JRace]

@mnrvovrfc : I made the modification for output file existence, refusing to do anything in that case. But it's what I chose to do.

That's the way I usually do it in programs I write for myself: if the program finds an error, it reports the error then aborts.

@bplus : This reminds me I need to update my own encryption code for spaces and punctuation...

Spaces?  Those were optional in TRS-80 Basic and I usually opted out, to conserve memory & diskette space.  Also, interpreted Basic programs were a couple percentage points faster without extra spaces.

I found the requirement for spaces to be quite annoying when I first took up GWBasic.