The `check_is_animated()` function will be used by the upcoming Alembic
exporter as well. There is nothing USD-specific in the function.
No functional changes.
The code was copied from the Alembic exporter, and some of the options are
no longer used.
Not updating the Alembic exporter itself, as this will be done in a much
larger rewrite.
printf is called for a size_t (64 bit on x64) type
but the formatter is `%lu` (32 bit) leading to a
warning with MSVC.
`%zu` is the appropriate formatter.
This moves the `alembic`, `avi`, `collada`, and `usd` modules into a common
`io` directory.
This also cleans up some `#include "../../{somedir}/{somefile}.h"` by
adding `../../io/{somedir}` to `CMakeLists.txt` and then just using
`#include "{somefile}.h"`.
No functional changes.
