Convert the source map spec to bikeshed with minor edits

[mitsuhiko]

Replaces tc39/ecma426#24

This is a transformation of the source map v3 with minimal edits to the .bs format, alongside with a Makefile to render it locally (make build and make watch).

Remaining work:

• indexed source maps are not addressed (same spec or separate spec?)
• reintroduce CSS references for sourceMappingURL
• who are the editors / former editors?
• set up github actions / publish to gh-pages

Changes made:

These (with the exception of the change to the URL standard) are marked in the document:

• JSON over HTTP Transport gives no longer relevant historic context to serving JSON over HTTP. Removed that reference but left the permission to prefix source maps with )]}' when served over HTTP.
• Clarified what a column is, specifically that this is counted in UTF-16 offsets which is what most tools do today. Tighten the definition of "column" ecma426#5
• Changed the URL reference to the WhatWG URL Standard
• Properly cited "Pavel Podivilov" (previously just mentioned as podivilov@)
• Removed the confusing HTTP header note ("An HTTP header would address this, but is not yet agreed upon.") as a SourceMap header is actually specified in the specification. Refs Do we support Multi-level mapping source map lookups for final source map consumption ecma426#11
• Strict reading of the spec allows multiple interpretations for version. I left a marked clarification there. This might be incorrect. See Hardening: version field ecma426#26

Followup work:

• Better explain what names is about. Document the meaning of the "names" array ecma426#6

Random notes:

• Not sure how the references should be done. Some references like sourceURL link to outdated resources. Maybe put into the spec?
• base64 and VLQ probably should be documented in the spec
• It turns out that web assembly source maps have a different proposed definition of a column. Is this canon? Should this be documented here? Source maps applied to wasm binaries WebAssembly/design#1051

Refs tc39/ecma426#23