Update change log for 0.2.1

In commit a1ca197 the version was supposed to be bumped to 0.2.0 but
was set to 0.2.1 instead.

The 0.2.0 tag was already pushed, so it can't be fixed now.

Make 0.2.1 instead with the couple of documentation fixes that have
been added since.

Change-Id: I70afb0de3124c03d957a8be0d54cabcceb5be9b8