docs: nit-picky documentation

* Adding nit-picky sphinx-build in travis build.
* Commenting out all the badly commented modules.
* Adding placeholder documents for missing pages.

**Build is failing**
```
FAIL: test_error_catching (invenio.modules.records.testsuite.test_record.TestMarcRecordCreation)

----------------------------------------------------------------------

Traceback (most recent call last):

File "/home/travis/build/greut/invenio/invenio/modules/records/testsuite/test_record.py", line 571, in test_error_catching

schema='xml'

AssertionError: ReaderException not raised
```
Indeed, I never bothered learning what were the rules behind this one.

>The handling of the `::` marker is smart:
> * If it occurs as a paragraph of its own, that paragraph is completely left out of the document.
> * If it is preceded by whitespace, the marker is removed.
> * If it is preceded by non-whitespace, the marker is replaced by a single colon.
>
> http://sphinx-doc.org/rest.html#source-code