Add option to enable old behavior

Cargo will use this in the interim.

src/parser.rs

@@ -89,6 +89,7 @@ impl Value {
 pub struct Parser<'a> {
     input: &'a str,
     cur: str::CharIndices<'a>,
+    require_newline_after_table: bool,
 
     /// A list of all errors which have occurred during parsing.
     ///
@@ -138,6 +139,7 @@ impl<'a> Parser<'a> {
             input: s,
             cur: s.char_indices(),
             errors: Vec::new(),
+            require_newline_after_table: true,
         }
     }
 
@@ -155,6 +157,16 @@ impl<'a> Parser<'a> {
         (self.input.lines().count(), 0)
     }
 
+    /// Historical versions of toml-rs accidentally allowed a newline after a
+    /// table definition, but the TOML spec requires a newline after a table
+    /// definition header.
+    ///
+    /// This option can be set to `false` (the default is `true`) to emulate
+    /// this behavior for backwards compatibility with older toml-rs versions.
+    pub fn set_require_newline_after_table(&mut self, require: bool) {
+        self.require_newline_after_table = require;
+    }
+
     fn next_pos(&self) -> usize {
         self.cur.clone().next().map(|p| p.0).unwrap_or(self.input.len())
     }
@@ -271,6 +283,7 @@ impl<'a> Parser<'a> {
                     values: BTreeMap::new(),
                     defined: true,
                 };
+                if self.require_newline_after_table {
                     self.ws();
                     self.comment();
                     if !self.newline() {
@@ -281,6 +294,7 @@ impl<'a> Parser<'a> {
                         });
                         return None
                     }
+                }
                 if !self.values(&mut table) { return None }
                 if array {
                     self.insert_array(&mut ret, &keys, Value::Table(table),