[fpc-pascal] Feature "Multiline strings" added

[Thomas Kurz]

> Deprecate in FPC and Pas2js the "backtick version". That is, let the
> compilers just generate a message like "Multi-line strings using
> backticks are deprecated and will be removed in some future release.
> We encourage to use instead syntax with 3 apostrophes, docs on XXX"
> when it encounters such syntax.
> And then it is clear to users what to use in new code. And they can
> easily upgrade their code, just follow compiler messages.
> And then in 2+ years maybe we can remove the old backtick version.
> And everything is simpler :)

+1 for this approach. I also think that only one way to do it may be the best. If pas2js was first, it'd be best to change Delphi, but it's pretty unrealistic. So migrating pas2js to the Delphi way seems to be the cleanest thing.

 Regards,
 Thomas