Added 'algorithm' and 'remove!' to BlobStore.

Added more tests for stores, including a re-usable function to
generically test the implementations of new blob stores.
Add tests for FileBlobStore.

For some reason, the `for-files` macro produces hundreds of unused forms
when nested, resulting in poor test coverage.
Simplify for-files a bit.
Add 'defprint-method' macro to vault.data ns.

This macro defines a standard print-method implementation for
TaggedValue types.
Shorten 'make-blobref' to '->blobref'.

This matches record constructors more closely, and also avoids clunky
attempts to avoid local 'blobref' symbols (like 'blob-ref', which
doesn't indicate as clearly that it's a factory function.