Refnx

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- Added DOTAP, h-DOPC, 18:1 Diether PC to lipids database
- Updated SLIM reduction software to cope with the new monobloc detector
- Improve speed of resolution smearing by using splev/splrep
- Added shell scripts to build manylinux and macOS wheels (as well as test
them).
- Some minor optimisations for calculation of `Interval.logp`.
- Some minor optimisations for various calculations in `Objective`.
- Fixed potential for crashes in ManualBeamFinder if controls specified
regions that went outside the detector region.
- cythonized contract_by_area, resulting in huge speedup for microsliced
structures.
- Enabled parallel calculation of reflectivity using OpenMP. Tests show that
it should be ~20% faster than the previous calculation in C.
- tqdm progress bar for ptemcee sampling (if tqdm is installed).
- Cleaned up the _creflect module. Threaded reflectivity calculation in that
extension now uses std::thread instead of pthreads (POSIX) or WinAPI
(windows).

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- When GUI experiment file is loaded the correct fitting algorithm wasn't being
set correctly (GH338).
- Prevent crash when trying to refresh a stale dataset (i.e. is no longer in
its original location.
- Produce autocorrelation graph when sampling in GUI.
- Added links to ptemcee and emcee in the optimisation parameters window.
- GUI produces corner plot after MCMC sampling
- BUG fix for rebinning code (doesn't affect analysis)
- Different interfacial roughness types can be specified between all Components
in a Structure. The available types are: Erf (Error Function, default), Tanh,
Sinusoidal, Exponential, Step, Linear. User specifiable interfaces can be
created by subclassing Interface.
- A fix for the PyQt5 interface using 4K screens on Windows was made.
Previously the GUI elements and fonts were being displayed in a much too
small fashion.
- Made various dialogues in the PyQt5 GUI window modal (to prevent them being
lost).
- fixed bugs if cancel was pressed during the MCMC folder dialogue phase.
- made loading of experiment file back compatible.

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- print human readable output when fitting with the Jupyter interactive
modeller.
- added shgo and dual_annealing minimiser options to the refnx gui.
- SLD calculator retains state between viewings.
- Added dialogue to adjust optimisation parameters.
- Fixed bug in export of MCMC code fragment, Gui would crash.
- Autocorrelation plot produced from mcmc.py code fragment, this can be used to
judge how much to thin the chains by.
- `refnx.analysis` now possesses a standalone function, `autocorrelation_chain`
for calculating chain autocorrelation. Previously the calculation had to be
done using a CurveFitter instance.
- Function for calculating autocorrelation time made visible as:
`refnx.analysis.integrated_time`. You should pass the autocorrelation array
to this function.
- GUI can now export an ASCII file representing the model SLD curve.
- BUG: when the GUI saves a model it should pickle a ReflectModel. It wasn't
doing this, it was pickling a DataObject. This has now been fixed, but the
fix affects back compatibility.
- *GUI can now do MCMC sampling*
- Add option to change context of Mapwrapper (spawn/fork/forkserver)
- BUG: when loading (not refreshing) a dataset that was already loaded, the
associated model was lost. (GH331)
- Added a progress bar for batch fitting.
- Speeded up batch fitting

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- When parameters are linked in the refnx GUI only the dataset containing the
master parameter was being updated (reflectivity/SLD curves) when the master
was changed. Now all datasets that have parameters linked to the master
parameter (a constraint) are updated.
- When a dataset/component/structure containing a master parameter (i.e. a
parameter to which other parameters are constrained to) is removed, the GUI
now unlinks those dependent parameters from the master parameter.
- display number of iterations in GUI progress box. If fit is aborted put best
fit so far into Objective that's being fitted.
- fixed crash resulting from the use of a comma when entering a floating point
number. Entering '3,1' would crash the gui, using '3.1' would work but be
displayed as '3,1'. The use of a dot as a decimal point is now enforced.

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- fixed font size in pyqt GUI.
- script export from pyqt GUI can use either multiprocessing or MPI for
parallelisation during MCMC sampling.
- speeded up reflectivity calculation, following on from changes made in 0.1.4
(if the imaginary part of a complex sqrt argument is very small, then the C++
calculation takes a lot longer).
- added a plot method to PlatypusNexus
- refactor util.PoolWrapper to util.MapWrapper
- allow the number of Stack repeats to be fittable.
- GUI option to only display those parameters (and datasets) that are going to
be varied in a fit.
- update testimonials.bib
- "to code" button in Jupyter interactive modeller respects the transform
popup.

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- fixed bug in reflectivity calculation with significant non-zero absorption.
The wavevector calculation was using the wrong branch of the complex sqrt.