Add the new Medeiros et al. error recovery paper.

Author: ltratt

softdev.bib

@@ -2292,3 +2292,11 @@ @book{parr13definitive
     publisher = "Pragmatic Bookshelf",
     isbn = "1934356999"
 }
+
+@article{medeiros19syntax,
+    author = "Medeiros, S\'ergio and de Azevedo Alvez Junior, Gilney and Mascarenhas, Fabio",
+    title = "Syntax Error Recovery in Parsing Expression Grammars",
+    month = May,
+    year = 2019,
+    url = {https://arxiv.org/abs/1905.02145}
+}