MOUNT to use Hypervisor v1.3 hyppo_attach

[dansanderson]

Is your feature request related to a problem? Please describe.
The MOUNT command uses Hyppo calls hyppo_d81attach0 ($40) and hyppo_d81attach1 ($46) to mount a disk image to drive 0 if U8 is given (or U is omitted or anything other than U9), or drive 1 if U9 is given, respectively. As of Hypervisor 1.3, these are deprecated in favor of hyppo_attach.

Furthermore, MOUNT manipulates the FDC directly to mount the internal floppy drive to drive 0. This should instead use the "detach" mode of hyppo_attach.

Describe the solution you'd like
Hypervisor 1.3 and hyppo_attach are expected to be in release v0.97. Wait until v0.97 is released, then replace both branches of the MOUNT implementation with calls to hyppo_attach.

Describe alternatives you've considered
We could add a generation of core compatibility by detecting the Hypervisor version and using the old code path for a version < 1.3. We don't normally do this (at least for 0.x releases so far) and instead simply expect anyone using a given stable ROM to use the core from the same stable release. ROM beta testers are expected to follow testing instructions with regards to cores.

We could go the other way and target the v0.97 release for this upgrade, with a temporary dependency from the ROM beta that implements this to the development core that provides hyppo_attach. As I write this, I'm expecting hyppo_attach and v0.97 to go out within a couple of months, and it's not an issue to leave the legacy ROM implementation in for this release and update it in v0.98.

Additional context
#192 is related but not the same issue because the "sticky" feature is not yet implemented in Hyppo 1.3.

(This issue does not request revising how the U argument to MOUNT is handled. I took a pass at writing up a feature request, then noticed that SET DISK does some interesting things with the virtual drives and I didn't want to mess with it. :) For the purposes of this issue, assume MOUNT already has a way to select between the two virtual drives.)

[nobruinfo]

@dansanderson It's worth mentioning that the current BASIC MOUNT has a huge advantage against mounting from within the freezer or via the above mentioned HDOS v1.3 functions: the mounts survive a side button inflicted machine reset. Let's try to add a feature not breaking that, shall we?

[dansanderson]

@nobruinfo That feature is orthogonal to this issue, and won't change with this. It's also incomplete and needs to be implemented in Hyppo to work properly: #192

[nobruinfo]

@dansanderson Of course these issue tickets serve different purposes. I was only feared we were about to take the last reset lasting MOUNT variant. Good to see there are tickets to circumvent this. Thank you for all your efforts, sir.