Fix docs for pin-arrow-line.
Filled out pin-arrow-label-line interface to match pin-arrow-line.
Make : error on unbound identifiers

Closes PR 13298
Fix error message for misuse of #:methods

Closes PR 14069
slideshow: fix letterbox clipping by avoiding offscreen mode
pict: restore use of loaded mask, if any, by `bitmap`

In case a `bitmap%` object with a mask is passed to `bitmap`.
repair for 5eee14032f

This repair needs a test case, but I think the test will require a lot
of scaffolding to set up a package configuration, so I'm leaving that
part on my todo list for now.
fix .zo marshal of a syntax object containing a hash table in a list

Also, fix `zo-parse` unmarshaling of syntax-object hash tables.

Closes PR 14087
Plot source reorg before separating "plot" into multiple packages

Also added plot/pict and plot/bitmap (and typed versions)
Split "plot" package into five packages
Removed dependency on "plot-compat" from "plot" package
Split "math" package into "math", "math-lib", "math-doc" and "math-test"
Use new plot/pict module for math docs
Fix props
Fix RacketCon link

(now that the main con link just aggregates the
 year pages, the old behavior is not useful)
Make references to fast-X in prose match fast-X in code.
TR for clause specialization: log syntax objects with location info.
TR for clause specialization: More detailed message.
TR for clause specialization: Report specialization failures.
slideshow: another attempt to fix letter box clipping

The workaround in 16552e9a67 wasn't right. This commit fixes
the bug, which was that the clipping region wasn't reset correctly,
instead f trying to work around it.