Link s4cmb Apps to a power-spectrum estimator

[JulienPeloton]

The difficulty here is to get something publicly available and easy/fast to run.
Reijo suggested using PolSpice.
I will give a try and report.

[smsimon]

Could also use David Alonso's code NaMASTER https://github.com/damonge/NaMaster. This may be a bit easier