v0.2.5

Implements Synod 0.2. Editors and learning modes: synod check can read unsaved
buffers and still colors a file that does not parse, lesson.Ask can offer
choices, and a run-time error inside std now points at the user's own code.

Added

• synod check --overlay <file> (synod-overlay/1): checks each listed .synod file or synod.mod as if it held the content of another file; diagnostics and tokens keep the original path and positions. A missing overlay, a bad format or a key that is not an existing file is exit 2.
• synod check --json --tokens lists lexical tokens (language, value, comment and name, without def) for a file that fails to lex or parse, for every other file of its package and for extra main files, so an editor keeps its highlighting while the user types.
• lesson.Ask [q: text] choosing [c: list of text] for Predict: 2 to 6 distinct, non-empty choices, else a bad-argument run-time error.
• scene.json shapes carry node and msg (the node or message a shape stands for), and pause markers carry choices when the question has choices.

Changed

• A run-time error raised while std code runs is reported at the position in user code of the call that entered std, in the trace (sim.Failed), the failed at and look failed at lines, the scene's failed marker and the rich form; the std position is kept as a note (decision 89). lesson.Ask … choosing with bad choices now points at the lesson.Ask call, not at std/lesson/lesson.synod.
• The trace record lesson.Asked gains the field Choices ({} for a plain lesson.Ask), so every trace and summary of a program with a question changes.