Pystra

Refactored isoprobabilistic transformation for extensibility & significant speed up.

What's Changed
* Update sorm.py by mhscott in https://github.com/pystra/pystra/pull/33
* Refactor Isoprobabilistic transformations by ccaprani in https://github.com/pystra/pystra/pull/37

New Contributors
* mhscott made their first contribution in https://github.com/pystra/pystra/pull/33

**Full Changelog**: https://github.com/pystra/pystra/compare/v1.1.0...v1.1.1

Breaking Changes:
- All analysis objects must now call a `run()` function to execute the analysis.
- Removed ability to call limit state function if passed as a string; use a function or lambda instead
- Default now is to not show printed results; use `options.setPrintResults(True)` to revert to previous behaviour. This makes the default behaviour better for using pystra in notebooks.

Updates:

- Added the Direct Differentiation Method (per https://github.com/pystra/pystra/issues/30 ), including a new example and tests.
- Progress on eliminating star imports
- Minor: changing `pr` to `ra` as shortform for pystra
- new `AnalysisObject` base class from which all probability estimators inherit
- Refactored `LimitState` so it now contains the evaluations of the LSF
- Multiple other minor tweaks.
- Update doc build requirements and fix some warnings

Pystra first release on pip. Pystra is a significant overhaul of the orignal `pyre` package by Jürgen Hackl and features:

- FORM and SORM structural realiability algorithms
- Sensitivity analysis
- All SciPy univariate continuous statistical distributions can be used
- Documentation significantly enhanced.