Make use of new mwalib >=v1.* exposed metafits attributes

[gsleap]

Build with mwalib >=1.0.0 and use the following newly exposed metafits values:

• Rfinput::rec_type which allows Birli to differentiate between the different receiver types (may or may not be useful right now)
• MetafitsContext::oversampled will allow Birli to alter the passband gains applied to each coarse channel as OS data will have very different values.
• MetafitsContext::deripple_applied and MetafitsContext::deripple_param will allow Birli to once again alter the passband gains applied to each coarse channel as the deripple will have very different values.

[cjordan]

This work ultimately requires Marlu to use the new mwalib. I can get started on this Soon™, maybe in a couple of days; I'm hoping to release the long-overdue hyperdrive 0.3.0 shortly.