fractional_resampler is a misnomer, should be renamed in next

[marcusmueller]

The blocks that we call fractional_resampler_{cc|ff} really shouldn't be called "fractional", as it suggests a rational in/output rate ratio. That's explicitly not the case with these. We have rational_resampler_ for that!

This has caused a lot of confusion among students, and newbies, in general. I'm not excluding myself here.

It's clear how that name "happened" – we have a (slightly confusingly named, but still in range of sensibility) fractional_interpolator. The fractional_resampler is basically the same thing.

I propose: we call that mmse_arb_resampler, to use the same naming logic than for pfb_arb_resampler and list them as "MMSE arbitrary resampler" in GRC.

Renaming the fractional_interpolator to mmse_interpolator would make sense, too.

[jmcorgan]

Agree. A PR to do this and change the QA, examples, and docs would be appreciated.