added change log

* version 2.0 (June 2, 2025)

	Summary of changes was made with the help of ChatGPT.

	Major changes:

		* NeXus NSE file support

		* modernizing the codebase (Qt6, Matplotlib3.0)

		* refactoring for modularity and maintainability.

	Cleanup & Refactoring:

		Various modules cleaned up (__init__.py, reduce.py, etc.).

		Reorganized and renamed several files for clarity (e.g., lib.py → spinecho.py, history.py → legacy_history.py, etc.).

		Moved constants and utility functions to more appropriate files.

		Consolidated/converged file conversion utilities: merged nxs2echo and convert2hdf.

	Physics & Math

		New & Updated Modules:

		Added physics/misc.py with conversion functions (tof2lambda, lambda2tof).

		Expanded nscatt.py with Zimm functions and updates to Rouse model.

		Improved mathutil.py with round_err.

	Plotting

		Refactored plotting into specialized modules (nseplotlib, nxsplotlib, qt3d, miscplotlib, etc.).

		Improved support for plotting NeXus-format files

		Fixed issues with colormaps and compatibility with newer Matplotlib versions.

		Enhanced xyz plots with error estimates and --details option.

		Introduced default modes for nseplot (e.g. center patch -C).

	Echo & Simulation

		Introduced SimpleEchoSimulator (renamed from SillyEchoSimulator).

		Improved simulator stability and added bug fixes.

		New spectrum_weighted_eshape function for simplifying energy shape analysis.

		Better handling of missing/invalid echo data (e.g. empty runs, missing currents).

	I/O & File Formats

		NeXus Integration:

			Full support for reading/writing NeXus files.

		New files: nexus.py, scans.py, nxs2taco.py.

		Conversion to legacy TACO-style files (echo, diffraction, transmission).

		Improved legacy HDF handling and transformation tools.

	UI/GUI Updates

		Qt6 Transition:

			Removed Qt5-specific dependencies.

		GUI reorganized and resources embedded into distribution.

		New UI modules: nsegui.py, nseplot.py, pyqtau.py.

		Improved error handling, plotting tools, and simulator UI.

	Bug Fixes & Improvements

		Fixed crashes on malformed data (e.g. missing flux, bad phase steps).

		Corrected i00 assignment in slowly changing SC current.

		Made test runs cleanly with pytest.

		Fixed normalization defaults (now pcharge for diffraction scans).

		Enhanced logging and removed unused imports.

	Testing & Infrastructure

		Test & Build Enhancements:

		Added pytest support.

		Included requirements in setup.

		Coverage reporting.

	Miscellaneous

		Added default diffraction normalization options.

		Improved error reporting and configuration sanity.

		Reworked detector coordinate mappings and readouts.