Pyerrors

Added
- `least_squares` and `total_least_squares` fits now have an optional keyword argument `num_grad`. If this argument is set to `True` the error propagation of the fit is performed via numerical instead of automatic differentiation. This options allows for fits functions which contain special functions or which are not analytically known.

Fixed
- Bug in `Corr.show` `comp` option fixed.

Added
- New submodule `input.pandas` added which adds the possibility to read and write pandas DataFrames containing `Obs` or `Corr` objects to csv files or SQLite databases.
- `hash` method for `Obs` objects added.
- `Obs.reweight` method added in analogy to `Corr.reweight` which allows for a more convenient reweighting of individual observables.
- `Corr.show` now has the additional argument `title` which allows to add a title to the figure. Figures are now saved with `bbox_inches='tight'`.
- Function for the extraction of the gradient flow coupling added (see 1607.06423 for details).
- `Corr.is_matrix_symmetric` added which efficiently checks whether a correlator matrix is symmetric. This is used to speed up the GEVP method.

Fixed
- `Corr.m_eff` can now deal with correlator entries which are exactly zero.
- Minor bugs in `input.dobs` fixed.

Fixed
- Further bugs in connection with correlator objects which have arrays with None entries as content fixed.

Fixed
- Bug in `Corr.matrix_symmetric` fixed which appeared when a time slice contained an array with `None` entries.

Fixed
- Bug in error propagation of correlated least square fits fixed.
- `Fit_result.gamma_method` can now be called with kwargs.

Added
- `obs.covariance` now has the option to smooth small eigenvalues of the matrix with the method described in hep-lat/9412087.
- `Corr.prune` was added which can reduce the size of a correlator matrix before solving the GEVP.
- `Corr.show` has two additional optional arguments. `hide_sigma` to hide data points with large errors and `references` to display reference values as horizontal lines.
- I/O routines for ALPHA dobs format added.
- `input.hadrons` functionality extended.

Changed
- The standard behavior of the `Corr.GEVP` method has changed. It now returns all eigenvectors of the system instead of only the specified ones as default. The standard way of sorting the eigenvectors was changed to `Eigenvalue`. The argument `sorted_list` was deprecated in favor of `sort`.
- Before performing a correlated fit the routine first runs an uncorrelated one to obtain a better guess for the initial parameters.

Fixed
- `obs.covariance` now also gives correct estimators if data defined on non-identical configurations is passed to the function.
- Rounding errors in estimating derivatives of fit parameters with respect to input data from the inverse hessian reduced. This should only make a difference when the magnitude of the errors of different fit parameters vary vastly.
- Bug in json.gz format fixed which did not properly store the replica mean values. Format version bumped to 1.1.
- The GEVP matrix is now symmetrized before solving the system for all sorting options not only the one with fixed `ts`.
- Automatic range estimation improved in `fits.residual_plot`.
- Bugs in `input.bdio` fixed.