Fix #303: Remove unused var *assert-not-standard-readtable*

Closes #303

See merge request !209

According to [fc0bd2a6] this change was supposed to be removed but
never was.  Let's do it now.  This was also the only place where we
used C++ comment-style.

Snapshots have been uploaded so use them for running the CI.

Fix #293:  Allow restarts for FP overflow in reader

Closes #293, #275, and #287

See merge request !201

Fix #275:  FP underflow in reader allows restart with 0

Closes #275 and #287

See merge request !197

Fix #296:  Fix disassembly of MOVD instruction

Closes #296 and #300

See merge request !207

Explain why we use `-V` for `bin/make-dist.sh`.  And instead of using
"ci-build" as the version, use `git describe --dirty` as the version.
This lets us know better what version was actually used for the build.

Fix #299: Use xoroshiro assembly routine for x86

Closes #299, #295, #300, #297, and #294

See merge request !208

Fix #298: Add with-float-rounding-mode macro

Closes #298

See merge request !205

Fix #294: Implement assembly routine for xoroshiro update

Closes #294

See merge request !202

Mention that the allowed values are the same as the values for the
rounding-mode in `set-floating-point-modes`.

Change indentation of docstring slightly so that it prints nicely via
`describe`.  (Emacs doesn't indent the docstring by the right amount
for `describe`.)

We renamed `old-rounding-mode` to `old-mode`, but forgot to update all
uses.

Fix #295:  Add docstring for define-assembly-routine

Closes #295

See merge request !204

Fix #300: Reduce code duplication in random

Closes #300

See merge request !206

Fix #297:  Print new-assem:assemble with less indentation

Closes #297

See merge request !203

No other changes.

Not 100% sure the expected results are right.  They seem plausible,
but I didn't actually analyze that the rounding is correct.

Add `ext:with-float-rounding-mode` macro to set the FP rounding mode
to be used when executing the body.

Forgot to add #288, #290, and #291 to the list of fixed issues.

Fix #291:  pprint handler-case neatly

Closes #291

See merge request !200

Fix #288: Re-enable deftransform for random integers

Closes #288

See merge request !198

Fix #290:  Neatly pprint with-float-traps-masked and friends

Closes #290

See merge request !199

Fix #287: Clean up make-float-aux

Closes #287

See merge request !196