Initial OHM grammar for extends tag

OHM is a PEG-based grammar parser generator which seems to be more
compatible with the Jinja language. We are not making use of their
automatic space handling since in Jinja whitespace is significant.

grammar/jinja.ohm

@@ -0,0 +1,34 @@
+Jinja {
+  Template
+    = expressions
+    
+    expressions
+    = expression*
+    
+    expression
+    = inlineStatement
+    
+    inlineStatement
+    = statementOpen sp? inlineStatementContent sp? statementClose
+    
+    inlineStatementContent
+    = statement_extends
+    
+    statement_extends
+    = statementId_extends sp stringLiteral
+    
+    statementOpen = "{%"
+    statementClose = "%}"
+    
+    statementId_extends = "extends"
+    
+    stringLiteral = stringLiteral_single | stringLiteral_double
+    
+    stringLiteral_single = quote_single (~quote_single any)* quote_single
+    stringLiteral_double = quote_double (~quote_double any)* quote_double
+
+	quote_single = "'"
+    quote_double = "\""
+
+    sp = (" " | "\t")+
+}