M0.9: figcraft-cli export names files as the app's export does (#1154)

export into a folder replaced every character outside letters, digits,
'-', '_', space and '.' with '_', so a frame called
"Homepage - desktop (live + verbeteringen)" became
"Homepage - desktop _live _ verbeteringen_.png". The app's
file.exportLayers keeps those names and only replaces what file systems
refuse. The CLI now uses the engine's safe_file_name, and docs/cli.md
says which characters are replaced.

Also adds my own entry to contributors/people.toml.

docs/cli.md

@@ -51,6 +51,10 @@ page 1 "Screens": 380 nodes, 4 top-level
 
 - `<out>` is a directory: one file per top-level frame of the page (default the first page), named
   after the frame (`Home.png`, `Settings.png`…); with no frames, one file per top-level layer.
+  The name is kept as it is, except for the characters file systems refuse (`/ \ : * ? " < > |`
+  and control characters), which become `_`, and leading or trailing spaces and dots, which are
+  dropped. The app's export replaces the same characters (there a `/` makes a folder). Two layers
+  with the same name get `Name 2`, `Name 3`…
 - `<out>` has an image extension: one file with the given `--node`, or the whole page composited.
 - `--node` takes a layer id (`12` or `0:12`) or a layer name.
 - `--format fig` (or an `<out>` ending in `.fig`) writes the whole file as `.fig`, experimental: