New features

Universal FEC encoder for binary linear codes
Utility functions for FEC to
- Convert parity-check matrix to generator matrix
- Make generator matrix systematic
- Generate dense Polar parity-check and generator matrices
- Verify that generator and parity check matrix are orthogonal in GF(2)
Linear interpolator for OFDM channel estimation (with optional time-averaging)
MIMO maximum likelihood detector that computes either LLRs on bits or logits on constellation points
SymbolSource layer for sampling arbitrary constellations
PAMSource layer for sampling PAM constellations
The SymbolSource, PAMSource, QAMSource, and Mapper optionally return the indices of the constellation points and/or the bit labels
Utility layer to compute logits on constellation points to LLRs on bits (with optional priors)
Utility layer to compute the mean and variance of a constellation given logits on the points
Addition of integration tests

Fixes