Use git tags for version information.

Extract version data from version.cfg.
Update MANIFEST.in to build valid source package.
Update dependencies and package metadata.
Remove subversion keywords and trailing whitespace.
Require Structure with new anisotropy handling.

Adjust PdfFitSandbox so that unit tests pass.
Do not use extra dependency_links.
Replace obsolete module matplotlib.numerix.
Use default fitrmin=0.5.

Starting from sensible default fit rmin is easier than setting
hard limits that open a can of worms for range handling in pdffit2.
Also add more detail to the error message that handles singular
matrix error.

This resolves #11.
Support diffpy.Structure 1.2 in the master branch.

This partially reverts commit 160b6ec7c84cfbfbcc0f9983c0f77c0000f409f2.