replace --mutable-type with --format in CLI commands

[warner]

To match the new webapi style, and to avoid interface churn in the future, I think we should change our CLI commands to use --format= instead of --mutable and --mutable-type= .

Of course --mutable will imply --format=SDMF, for backwards compatibility. (we could argue that --mutable should mean "use whatever your gateway's default mutable format is", but that either requires that the CLI tools use the now-deprecated mutable=true queryarg, or we invent a fourth value for the format= queryarg which means "your default mutable type", and I think that simply implying SDMF is easier)

[Brian Warner <warner@…>]

In 3eb60ff986563e79:

add --format= to 'tahoe put'/'mkdir', remove --mutable-type. Closes #1561

[Brian Warner <warner@…>]

In 57ee56533f9a7854:

(The changeset message doesn't reference this ticket)

[Brian Warner <warner@…>]

In [5508/ticket999-S3-backend]:

add --format= to 'tahoe put'/'mkdir', remove --mutable-type. Closes #1561

[Brian Warner <warner@…>]

In [5509/ticket999-S3-backend]:

CLI: don't deprecate --mutable, small docs fixes. refs #1561

Also don't accept 'tahoe mkdir --format=chk'.