Add single line comments to grammar

Currently our syntax does not allow any kind of comments. Introduce
single line comments into parser grammar.

src/parser.pegjs

@@ -42,10 +42,13 @@
 }
 
 Start
-  = LineTerminator* first:Line tail:(LineTerminator+ Line)* LineTerminator* {
+  = EndOfLine* first:Line tail:(EndOfLine+ Line)* EndOfLine* {
     return start(first, tail);
   }
 
+SourceCharacter
+  = .
+
 WhiteSpace
   = [ \t]+ ('\\' LineTerminator+ [ \t]*)?
 
@@ -56,6 +59,13 @@ LineTerminator
   / '\u2028'
   / '\u2029'
 
+EndOfLine
+  = LineTerminator+
+  / SingleLineComment+
+
+SingleLineComment
+  = '#' (!LineTerminator SourceCharacter)*
+
 Word
   = id:[^ \t\r\n\u2028\u2029;:\\#]+ WhiteSpace? {
       return id.join('');