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* **[breaking change]** `theta` field in `extract()` output is now in
radians rather than degrees, for compatibility with new ellipse
aperture functions.
* **[deprecation]** Change `mask_ellipse()` parameters from ellipse
coefficients to ellipse axes and position angle, to match aperture
functions. (Old behavior still works as well.)
* **[deprecation]** Change `apercirc()` to `sum_circle()`, to match
new aperture functions. (Old name, `apercirc()`, still works.)
* Add `sum_circann()`, `sum_ellipse()`, `sum_ellipann()`,
`kron_radius()`, `ellipse_coeffs()`, `ellipse_axes()` functions.
* Exact mode aperture photometery in all functions, with `subpix=0`.
* Enable variable thresholding in `sep.extract`. [11]
* Fix bug in background masking. This bug impacted masking in all
functions that used masking. Also affected C library.
* More detail in error messages coming from within the C library.
More helpful error message for non-native byteorder arrays.
* Add ability to change pixel stack size used in `extract()`, with
`set_extract_pixstack()` function