Reworked impl of iRRAM::stiff and removed stiff_{begin,end}().
Explicit use of iRRAM::stiff computation in sin_range_red1(), also 'sin_sign' does not need to be REAL.
Unexport symbols 'ln2_val' and 'ln2_err'.
Merge branch 'master' of github.com:norbert-mueller/iRRAM