v0.1.0

First stable release. The API, the file format (kind ioscene, format 1) and the validation codes are those of
0.1.0-preview.2. From this release a patch adds or fixes; a breaking change waits for 0.2.0 (docs/contract.md,
section 5). A package that depends on IOScene references [0.1.0, 0.2.0-0).

Changed

• README, docs/contract.md and SECURITY.md describe a stable package, and the install command has no
  --prerelease.
• docs/contract.md and the XML documentation state these rules; the code is unchanged:
  • An explicit null reads as the default for text other than Kind, lists, objects and members marked ?.
    SceneJson.Read rejects a null for a number, an enum, a math value, a date-time or a property value
    with InvalidDataException.
  • Validate() does not check vertex-count and index-count for a topology it does not know; index-range,
    normal-count and uv-count apply to every topology.
  • A triangle's front is the side from which its vertices run counter-clockwise, and normals point to the front. An
    instance transform with a negative determinant reverses the winding (the glTF rule).
  • A PlannedStart or PlannedEnd at its default 0001-01-01T00:00:00+00:00 means "not given"; a consumer leaves
    such a task out of time-based views.
  • Date-times are written with an offset; a value without one is read in the local time zone.
  • SceneModel.Producer is the package id and the NuGet version without build metadata, separated by one space.
  • An instance colour replaces the material colour, also as the factor of the material's texture.
  • A lookup by key takes the first property with the key in the first set that has it.
  • SceneJson writes and reads JSON nested at most 128 levels deep, which holds 62 levels of tasks.
• docs/keys.md: the namespaces revit: and ifc: are registered; their formats are fixed from the first releases
  of RvtIO.Scene and IfcIO.Scene. Shared, project and family parameters have no key yet.
• The package has its own icon instead of a copy of the IOViewer icon.