Changes for tf0.12 (GPflow#307)

* Changes for tf0.12.

* Modified tests as well, updated readme & version.

* Update .travis.yml

Incrementing minor version number to 0.3.4 (GPflow#262)

* Incrementing minor version number.

* Correcting typo.

v0.3.3 paper submission. (GPflow#243)

Merge pull request GPflow#238 from GPflow/versionupdate3.2

Versionupdate3.2

Tf wraps (GPflow#198)

* Renaming tf_hacks to tf_wraps

* Changing tf_hacks to tf_wraps in code.

* adding a tf_hacks file that raises deprecationwarnings

* release notes

* bumpng version on docs

* importing tf_hacks, tf_wraps

Fixes GPflow#161 (GPflow#164)

* Fixes GPflow#161

* pep8ified test_likelihoods