scribble/srcdoc: add `form-doc`
optimizer: transform ((begin ... proc) x) to (begin ... (proc x))

Currently the optimizer can convert ((let (...) ... proc) x) to
(let (...) ... (proc x)). This is useful especially if proc can be
inlined. Extend this to begin's forms.
optimizer: another ((begin ... proc) x) to (begin ... (proc x))

The tranformation this time applies before optimization of the rator
and complements Gustavo's variant, which applies after optimization of
the rator.
add an optional argument example to ->i docs
optimizer: Remove unused flag added in d14b4a8
racket/gui: change placement of children in `panel%` and `pane%`

The `panel%` and `pane%` classes were not originally intended for
direct instantiation; instead, `horizontal-pane[l]%` and
`vertical-pane[l]%` provide basic placements that make sense for
multiple children. Adjusting `pane[l]%` to just overlay all children
seems both sensible and useful (if only one child is shown at a time,
for example).

As suggested by David Nelson.
RacketCon schedule.
raco setup: fix ".dylib" references on install

If a Mach-O file installed with `{copy,move}-foreign-libs` has a
"@loader_path/" reference to a library that is installed in a
different target directory (normally because it's from a package that
is installed in a different scope), then change "@loader_path/" to an
absolute-path reference to that target.
Treat fully-annotated plain `define` as an annotated defintion.

Fixes most of PR 14702.
Link talks in schedule with their description.
optimizer: use the equal? => eq? transformation to the optimizer phase

For some types, (equal? x y) is transformed into (eq? x y) in the resolve phase.
This commit adds this transformation to the optimizer phase. This improves
constant folding and enable some optimizations that are prevented
because equal? can run arbitrary code.

Also, transform   (eq? #f x) => (not x)   and   (eq? '() x) => (null? x)   to use
the type information of x when it's known.
ffi/unsafe: changed the way `ffi-lib` uses a version number with ".dll"

Add the version with a "-" before ".dll", instead of with a "."
after ".dll".