v.1.13.0.0.

v1.13.0.0

New features

1. sight improvements for bernstein
2. disable Thiele rational interpolation from the tests. Sometnjug wrong with the code.
3. extend a bit functionality of asymmetric errors (needed for graphs&plots)
4. collect pretty-print functions into new module ostap.logger.pretty
5. extend and improve pretty-print stuff
6. make the dbase.Item a bit lighter
7. For shelve-like databases: allow to specify the preferred backend as dbtype = ...
8. reimplement SqliteShelf as ZipShelf with dbtype='sqlite'
9. eliminate messy stuff with extensions for `XXXShelf``-classes

Backward incompatible

Bug fixes

1. fix a minor bug in bernstein.solve
2. fix couple of recent bugs in `histos