Myokit

- Added xNES and SNES optimisation methods.
- Added interface to CMA-ES optimisation method.
- Replaced the 'tolerance' arguments `in myokit.lib.fit` with more accurate counterparts.
- Removed `ga()` optimisation method.

- Added model export to Stan.
- Added data-clamp to CVODE simulation (works, but generally a bad idea).
- Added Protocol.add_step convenience method for building sequential step protocols.
- Added `log()` method to `ExportError`.
- Fixed bug in ABF reading (ABF channel index can be greater than number of channels in file).
- Small fixes to `DataLogViewer`.
- Fixed issue with PySide file open/save dialogs.
- Several small fixes to docs.

- Bugfix in PyQt4 support.

- Fixed PyQt4/5 and PySide compatibility issue that was causing errors in the DataBlock viewer's open function.

- Added missing pragma directive to enable double-precision simulations OpenCL.

- Added support for PyQt5.