Add possibility to use FFTW for OfdmGenerator
Make KISS entirely optional

The Resampler block can also use fftw, and the Makefile only
does the kiss fft compilation when --enable-fftw is not given.
Update INSTALL and mention FFTW
Refactor autoconf, make FFTW default
Correct autoconf for FFTW
Add autoconf check for pthread
Add new ZeroMQ IQ output
Fix compilation without zmq output
Change UHD txgain to double
Remove Makefile.am UHD check
Update configuration example
Update -V output
Print compile-time settings on startup
Interpret a single cmdline option as ini file name
Markdownise README
Prepare v0.5.0