update the doc and api doc to 1.2b2
link installation in doc to README.rst on github
Use version.cfg when git is not installed
Remove obsolete examples for a tagged release.

Will be reworked later.
Add Lattice attribute isotropicunit.

isotropicunit is an isotropic ADP matrix in the given coordinate system.
Add method isanisotropic to the Lattice class.

This checks whether a 3x3 ADP matrix is anisotropic.
Avoid roundoffs for Uisoequiv from isotropic matrix.
Show warning do not crash for missing version.cfg.

Also use RawConfigParser to avoid "%" interpolations.
Add fallback version.  Support commit metadata for git archive.

Switch to RawConfigParser to avoid issues with "%" interpolation.
Add commit metadata that expand for git tarball.
Improve resolution of version metadata.

Use gitarchive.cfg first, then git describe.
Do not export git-related files.
Avoid rewriting version.cfg with empty git data.