this is just a quick hack unfortunately; the code and in particular
diagram settings require a major revision

The log_frequency scale cannot contain exactly the requested number of
values for the lowest decade. This test mode allows to check whether the
higher value decades are affected by this. They are not.

The reason for not producing the requested number of value is, that the
smallest frequency on the logarithmic scale than would be smaller than
the smallest value on the linear scale. So log_frequency lets the
smallest value of the logarithmic scale be as small as the smallest
value of the linear scale, but not smaller.

In cases, where no PSD is required, the PSD computation is skipped. This
was not properly accounted for in the checks done in the program:

PSD is not required for transfer of phase and the existence of these
value shall not be checked in these cases; check for frequency array
being smaller than 2 (rather than 1); add verbosity output

- use correct way of specifying units
- avoid Hollerith constants

This is necessary to make to read member functions available which
previously where presented in sfftsfile.h

Code is reorganized in compilation units in smaller granularity.

The idea of providing inputoperators.h and outputoperators.h is to allow
to load the classes from modules in this library without loading all
input and output stream operators. Since sff::ts::File<C> provide member
functions for reading, this cannot be implemented strictly.

This is the first commit in a series of commits to fix a major bug:

Currently the source code fails to compile with g++ 7.3.1, although no
fatal errors were reported with previous compiler versions. Code
analysis reveals:
line 139 in sfftsfile.h calls the input operator
  datrw::idatstream& operator>>(datrw::idatstream& is, FileHeader& fh);
which is not available there. It is embarrassing that this went
unnoticed for such a long time. The input operator cannot be made
available there because of inappropriate separation of class declaration
and member function implementation. sfftsfile.h contains a declaration
required by inputoperators.h Hence sfftsfile.h amy not load inputoperators.h

Currently inputoperators.h appears like the main interface to libtsioxx,
loading all other header files subsequently. This appears inapprorpiate
as well.

The code must be reorganized in different compilation units, probably
introducing smaller granularity. This will change the API to the library
in terms of header files.