Close 2.3.0: date the changelog and ship the analyzer release #174

Release steps 2 and 3 of CONTRIBUTING's "Releasing" for 2.3.0:

• CHANGELOG.md: the 2.3.0 section dated, its links pointed at blob/v2.3.0/.
• AnalyzerReleases.Shipped.md: a ## Release 2.3.0 section. 2.3.0 adds no rule (CMTK0003 and CMTK0009 widen rules shipped earlier), so it is empty and Unshipped.md already is.

Step 1 runs locally on release/2.3.0 at 49be869: docs-query due --nuget lists no fact due (0 of 34), and oracles seeds runs before the tag.