PEG deprecations1--tjl: Deprecating old stuff, round 1

There is some crud in Alph left over from long times ago. Let's get rid of it.

Issues

System Message: ERROR/3 (../ffdoc/alph/pegboard/deprecations1--tjl/peg.rst, line 14)

Section empty; must have contents.

Deprecate (and remove ASAP)

Span1D.getRelativeStart(Span1D)
Span1D.getRelativeEnd(Span1D)

Nothing uses those methods and they're easy to reproduce outside the spans if ever needed.