freqmodem: removing option for demod type: fixing as delay-conjugate
freqmodem: adding freqmod benchmark
freqmodem: adding freqdem benchmark
freqmodem: removing pre/post and RF filters

  * trying to condense frequency modulation to its bare essentials
  * performance can be greatly improved with filtering, but that is
    really outside the scope of the freqmodem objects
  * with upcoming block-level processing, filtering should be much
    easier to implement
freqmodem: simplifying modulator

  * removing trapezoidal integrator (iirfilt_rrrf object)
  * replacing with simple rectangular integrator
  * easier to understand
  * adds single sample delay (rather than 1/2 sample delay with
    trapezoidal integrator)
  * minimal performance loss
  * symmetric with demod using single-sample differentiator
freqmodem: adding methods to modulate, demodulate block of samples
freqmodem: running actual autotest checks

  * simply comparing demodulator output to original signal
  * using rectangular integrator, output message has zero delay
  * only first sample needs to be ignored
freqmodem: using fixed-point phase for modulation

  * allocate sin|cos look-up table with 10 bits of precision
  * takes a performance hit in terms of output fidelity
  * no longer need to worry about long-term phase accumulation errors
    with floating-point phase
freqmodem: cleaning demodulator code of cruft
Merge branch 'freqmodem-dev'