filter/resamp2: changing center frequency variable, 'fc' -> 'f0'
Merge branch 'master' of liquidsdr.org/liquid-dsp
agc: adding real input/output example program
Merge branch 'master' of liquidsdr.org/liquid-dsp
math: moving all complex trig method prototypes to internal header

  * no public methods ever defined as returning complex type
  * should simplify C++ linkage
  * had been an issue with certain compilers (e.g. clang)
build: adding clause for _LIBCPP_COMPLEX in global header

  * adds support for libc++ and clang for external linkage
  * clang still throws a ton of warnings with regard to functions
    returning complex types (e.g. liquid_float_complex)
  * only an issue with return types; not sure why compiler doesn't
    complain when passing liquid_float_complex to functions as arguments