Added BibTeX hidden block (alshedivat#293)

* Added BibTeX hidden block

* Minor adjustments

Co-authored-by: Maruan Al-Shedivat <alshedivat.maruan@gmail.com>

Author: afonsocraposo

_bibliography/papers.bib

@@ -4,6 +4,7 @@
 @string{aps = {American Physical Society,}}
 
 @book{einstein1956investigations,
+  bibtex_show={true},
   title={Investigations on the Theory of the Brownian Movement},
   author={Einstein, Albert},
   year={1956},
@@ -12,6 +13,7 @@ @book{einstein1956investigations
 
 @article{einstein1950meaning,
   abbr={AJP},
+  bibtex_show={true},
   title={The meaning of relativity},
   author={Einstein, Albert and Taub, AH},
   journal={American Journal of Physics,},

_layouts/bib.html

@@ -86,6 +86,9 @@
     {% if entry.arxiv %}
       <a href="http://arxiv.org/abs/{{ entry.arxiv }}" class="btn btn-sm z-depth-0" role="button" target="_blank">arXiv</a>
     {% endif %}
+    {% if entry.bibtex_show %}
+        <a class="bibtex btn btn-sm z-depth-0" role="button">Bib</a>
+    {% endif %}
     {% if entry.html %}
       <a href="{{ entry.html }}" class="btn btn-sm z-depth-0" role="button" target="_blank">HTML</a>
     {% endif %}
@@ -134,5 +137,12 @@
       <p>{{ entry.abstract }}</p>
     </div>
     {% endif %}
+
+    <!-- Hidden bibtex block -->
+    {% if entry.bibtex_show %}
+    <div class="bibtex hidden">
+      {% highlight bibtex %}{{ entry.bibtex }}{% endhighlight %}
+    </div>
+    {% endif %}
   </div>
 </div>