Release 4.0.0: the Sea Update — galleon, steamer, sloop, tug, and a dolphin

The rails now end at a shoreline. Four vessels join the roster with an
animated sea (swell pattern, glints, hull bob, bow spray, stern wake),
a flapping Jolly Roger and turning paddle wheel on the same 4-frame
machinery as the locomotive wheels, per-vessel liveries and whistles,
an iceberg finale for -a at sea, the Flying Dutchman for -F, and -d,
which summons a dolphin that dives ahead of the ship on the angle its
art was drawn at. The tug travels diagonally for the same reason.

Also ships the outstanding audit fixes: smoke lingers after the train
exits, narrow-terminal crashes stay on-screen, -t fully overrides -l,
make demo runs the train it advertises, --speed documents its clamp,
CODE_OF_CONDUCT.md exists, LICENSE year range updated.

CODE_OF_CONDUCT.md

@@ -0,0 +1,65 @@
+# Code of Conduct
+
+## Our Pledge
+
+We as members, contributors, and leaders pledge to make participation in the
+sl community a harassment-free experience for everyone, regardless of age,
+body size, visible or invisible disability, ethnicity, sex characteristics,
+gender identity and expression, level of experience, education,
+socio-economic status, nationality, personal appearance, race, religion, or
+sexual identity and orientation.
+
+We pledge to act and interact in ways that contribute to an open, welcoming,
+diverse, inclusive, and healthy community. The train carries everyone.
+
+## Our Standards
+
+Examples of behavior that contributes to a positive environment:
+
+- Demonstrating empathy and kindness toward other people
+- Being respectful of differing opinions, viewpoints, and experiences
+- Giving and gracefully accepting constructive feedback
+- Accepting responsibility and apologizing to those affected by our
+  mistakes, and learning from the experience
+- Focusing on what is best not just for us as individuals, but for the
+  overall community
+
+Examples of unacceptable behavior:
+
+- The use of sexualized language or imagery, and sexual attention or
+  advances of any kind
+- Trolling, insulting or derogatory comments, and personal or political
+  attacks
+- Public or private harassment
+- Publishing others' private information, such as a physical or email
+  address, without their explicit permission
+- Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Enforcement Responsibilities
+
+Project maintainers are responsible for clarifying and enforcing our
+standards of acceptable behavior and will take appropriate and fair
+corrective action in response to any behavior that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies within all community spaces (issues, pull
+requests, discussions), and also applies when an individual is officially
+representing the community in public spaces.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported to the maintainer at
+[contact@stevenmilanese.com](mailto:contact@stevenmilanese.com).
+All complaints will be reviewed and investigated promptly and fairly, and
+the privacy and security of the reporter will be respected.
+
+## Attribution
+
+This Code of Conduct is adapted from the
+[Contributor Covenant](https://www.contributor-covenant.org), version 2.1,
+available at
+https://www.contributor-covenant.org/version/2/1/code_of_conduct.html.