Spaces in Change Block in PAE2

[ahankinson]

From rism-digital/pae-code-spec#91

The PAE2 specification will change the format of the "clef / timesig / keysig" change section to not allow spaces between "change statements". Currently Verovio flags no spaces as a warning for PAE1.

Once this change is ratified in PAE2, we'll need to update Verovio to fix it. If the change is not ratified, then we can close this issue.

So this is here as a reminder for future us.

[lpugin]

Since single-line PAE input has never been officially documented outside Verovio, we can go ahead with this. I would suggest for Verovio not to make a distinction between PAE1 and PAE2 here.