Store git version data in a configuration file.
Use "covalent" as a string type id for CovalentRadiiTable.

tb = AtomRadiiTable.createByType('covalent')
makes more sense than
tb = AtomRadiiTable.createByType('covalentradii').
Add EMPTY constant for a singleton empty structure.
Fix PairQuantity.getStructure().

Python could not represent constant StructureAdapter.
Remove constness in a method wrapper.
Rename PeakProfile.yvalue --> PeakProfile.__call__.

Interface cleanup - let's use the PeakProfile class as a functor
whose instances can be directly called.
Fill docstrings for PDFEnvelope classes.
Fill in docstrings for PeakProfile class.
Add explicit peakprecision property to PeakProfile.
Improve module description, remove surplass imports.
Add wrapper for PeakProfile.ticker() method.
Fill docstring for PeakWidthModel.ticker().
Fill docstrings for PeakWidthModel classes.

Also add property wrappers for the ConstantPeakWidth and JeongPeakWidth
classes.
Decorate function end with return.

No change in code function.
Fix for use of non-constant StructureAdapterPtr.

This reverts commit 85d08d66351f7d7bf6f97eaf887d508515264574
and 78c7d72733dd47f0298304f790e6caaf034b07a4.
Use shared helpers _pickle_getstate, _pickle_setstate.

No need to define the same code several times.
Improve PDFBaseline pickling.

Wrappers to C++ classes should not pickle wrapper __dict__,
it has no use.
Add pickling support for PeakWidthModel class.
Add docstrings for PDFEnvelope classes.
Clean up pickling for ScatteringFactorTable.
Clean up the _registerDoubleAttribute wrap.

Move python code to python file.