Update CHANGES for 3.2.0

[mloskot]

Update the CHANGES file with major fixes and new features in SOCI 3.2.0, extract release notes.

BTW, may switch to Markdown, nice example here bootstrap/CHANGELOG

[mloskot]

Done in f111963

I haven't changed the file format, it may change in future.
Meanwhile, if anyone wishes to generate complete, pretty and clickable changelog, git can do it:

• add alias, i.e. git ghclm for GitHub ChangeLog Markdown generator

$ git config --global alias.ghclm
!sh -c 'git log $1...$2  --pretty=format:"* [view](http://github.com/$3/$4/commit/%H) - %s"' -

• Generate all changes since SOCI 3.1.0 until 3.2.0 (empty `''`` stands for non-existing current tag):

git ghclm 3.1.0 '' SOCI soci > soci-3.2.0-github-changelog.md

Gist with output example is here soci-3.2.0-github-changelog.md