[SCons/Doc] Fix installation of Doxygen docs

Fixes regression introduced in b84d3e3, where the organization of files in the built
documentation changed.

Fixes Cantera#553

[Doc] Update versions of Ubuntu for which Cantera is packaged

We can no longer build on stock 14.04 due to the requirement for Cython >= 0.23.

[CI] Return exit code from 'scons test' to make Appveyor status correct

Resolves Cantera#382

[Doc] Update branch in git checkout instructions to 2.2

Bump version to 2.2.0

Bump version to 2.2.0b1

[Doc] Add installation instructions for Ubuntu PPA

Cherry-pick of trunk r3164.

Fix version displayed by Doxygen docs

Bump version to 2.1.0

Bump version for 2.0.2 maintenance release