ChebyCoeff -> ChebyExpan

  ComplexChebyCoeff -> CmplxChebyExpan

  BasisFunc -> VectorChebyExpan

  change ComplexChebyExpan so that f[n] = z works.

x change states to that Physical/Spectral

x change DNSFlags to enums instead of bools

  better name for DNSFlags (match NSIntegrator name).

  ask dietmar about use of q/p for modified pressure

. choose good filename extensions for output files

  add gridpoints() to ChebyCoeff

x change flowfield::fourierCoeff to somethign better, shorter.

x regularize x y z states or xz y states

  Use "method" whenever it's apt. Explain somewhere.

  Add Vector {x,y,z}gridpoints() method to FlowField, ChebyCoeff.

  Logo,icon for channelflow.

x regularize nonbinary DNSFlags

  check that time-varying bulk vel and press grad work properly

x write example for RK3 start-up of a CNAB2 integration.

  how does NSIntegrator dPdx deal with modified pressure?

  revise NSIntegrator::advance to match docs on constraint-matching

  put CNAB2 check in NSIntegrator::advance(u,q,ubulk) 

  change FlowField and Chebyshev IO to print S/P.

  regularize FlowField slice and profile functions

  change BasisFunc to VectorChebyCoeff?

  elementary differentiaion functions on FFs.

x .bff -> .ff

  resetUbulk -> reset_ubulk

  maybe rename TauSolver

  move dPdx,Ubulk to DNSConfig and change way NSIntegrator deals w them

  remove kx=kz=0 perturbations from addPerturbations

  check skewsymmetric