backfill DOIs for previous releases

Author: njsmith

doc/changes.rst

@@ -45,6 +45,9 @@ v0.3.0
 v0.2.1
 ------
 
+.. image:: https://zenodo.org/badge/doi/10.5281/zenodo.11447.png
+   :target: http://dx.doi.org/10.5281/zenodo.11447
+
 * Fixed a nasty bug in missing value handling where, if missing values
   were present, ``dmatrix(..., result_type="dataframe")`` would always
   crash, and ``dmatrices("y ~ 1")`` would produce left- and right-hand
@@ -60,6 +63,9 @@ v0.2.1
 v0.2.0
 ------
 
+.. image:: https://zenodo.org/badge/doi/10.5281/zenodo.11448.png
+   :target: http://dx.doi.org/10.5281/zenodo.11448
+
 Warnings:
 
 * The lowest officially supported Python version is now 2.5. So far as
@@ -92,4 +98,8 @@ Other: miscellaneous doc improvements and bug fixes.
 
 v0.1.0
 ------
+
+.. image:: https://zenodo.org/badge/doi/10.5281/zenodo.11449.png
+   :target: http://dx.doi.org/10.5281/zenodo.11449
+
   First public release.