message: Documented recent changes involving Array class.
diff: @@ -18,6 +18,8 @@ The Axom project release numbers follow [Semantic Versioning](http://semver.org/
  - Added support for face data and face connectivity in the mint StructuredMesh classes.
  ### Removed
  +- Moved mint::Array to axom::Array with sidre storage in sidre::Array;
  + also moved mint::IndexType to axom::IndexType.
  - Replaced sidre::SidreLength with sidre::IndexType.
  - Replaced usage of std::size_t in sidre with sidre::IndexType.
  - Added AXOM_ENABLE_EXPORTS which enables CMAKE_ENABLE_EXPORTS to allow demangled
  