GitLab

Add license headers, fix some macOS issues

`tf.mul` -> `tf.multiply`

SyntaxNet does not compile with gcc version 5.4.0 20160609 (Ubuntu
5.4.0-6ubuntu1~16.04.4). This leads to the error in #1194.

Including cmath and using the std namespace for isnan solves this
problem.

Some further links fixes

The `center` tag would cause the image not to be rendered, but the raw text to be inserted. Simply removing the center tag fixes this.

Second row had an extra set of dashes, making the markdown invalid and falling back to raw text instead of the intended table.

Update the encoding instructions

Minor fix to skip_thoughts documentation.

Update citation

Implementation of Skip Thought-Vectors model

* Release DRAGNN

* Update CoNLL evaluation table & evaluator.py

* Update documentation & tutorial for DRAGNN

* Update the DRAGNN

* Tutorial link

Remove code and append flag warning

Add case for compiling ops if tensorflow was compiled from source using gcc >= 5.0