Add input validation to all scripts

[bertfrees]

• Should validation be an option or should it be enabled always?
• Do all scripts need a assert-valid option, or is it always true for some scripts?

See original request by Tuomas Kassila on the mailing list:

Hi, script dtbook-to-daisy3 is missing --assert-valid option! Not all dtbooks or another input files with diff. scripts are validated files! Could you add --assert-valid true option into next scripts:

dtbook-to-daisy3 script html-to-epub3 dtbook-to-zedai epub3-to-daisy202 zedai-to-html daisy3-to-daisy202 html-to-pef zedai-to-epub3 epub3-to-pef daisy202-to-epub3

And the same options into all clients.

Thanks,

Tuomas

[bertfrees]

The assert-valid option is already present in these scripts:

• daisy3-to-epub3
• dtbook-to-epub3
• dtbook-to-html
• dtbook-to-zedai