Add one-variable-per-declaration tslint rule

Multiple declarations per line makes it more difficult to read what
exactly is declared and generally makes code more verbose and less
likely to fill in types

src/Parser.ts

@@ -182,7 +182,12 @@ export class Parser {
    * @param data The data to parse.
    */
   public parse(data: string): ParserState {
-    let l = data.length, j, cs, ch, code, low;
+    const l = data.length;
+    let j;
+    let cs;
+    let ch;
+    let code;
+    let low;
 
     if (this._terminal.debug) {
       this._terminal.log('data: ' + data);