Change syntax Pos to use 1-based indices for lines and columns by default

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/span.rs

@@ -8,11 +8,12 @@ pub struct Pos {
     pub col: usize,
     pub byte: usize,
     pub len: usize,
+    pub is_newline: bool,
 }
 
 impl Display for Pos {
     fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
-        write!(fmt, "line {} at {}", self.line + 1, self.col + 1)
+        write!(fmt, "line {} at {}", self.line, self.col)
     }
 }
 
@@ -20,10 +21,11 @@ impl Default for Pos {
     fn default() -> Self {
         Pos {
             source: 0,
-            line: 0,
-            col: 0,
+            line: 1,
+            col: 1,
             byte: 0,
             len: 1,
+            is_newline: false,
         }
     }
 }
@@ -43,13 +45,14 @@ impl Pos {
             col,
             byte,
             len: c.len_utf8(),
+            is_newline: c == '\n',
         }
     }
 
     pub fn next_char(&self, c: char) -> Self {
         Pos {
             source: self.source + 1,
-            line: if c == '\n' {
+            line: if self.is_newline {
                 self.line + 1
             } else {
                 self.line
@@ -57,6 +60,7 @@ impl Pos {
             col: self.col + 1,
             byte: self.byte + self.len,
             len: c.len_utf8(),
+            is_newline: c == '\n',
         }
     }