Add no-unused-variable rule

test/rules.out

@@ -1,9 +1,11 @@
 
 ERROR: rules/curly.ts[4, 3]: if statements must be braced
 ERROR: rules/handle-callback-err.ts[1, 21]: Expected error to be handled
+ERROR: rules/import-spacing.ts[2, 1]: All imports are unused.
 ERROR: rules/import-spacing.ts[1, 7]: missing whitespace
 ERROR: rules/no-constant-condition.ts[1, 5]: unexpected constant condition
 ERROR: rules/no-inner-declarations.ts[4, 20]: block is empty
+ERROR: rules/no-inner-declarations.ts[4, 12]: 'test' is declared but never used.
 ERROR: rules/no-inner-declarations.ts[4, 3]: move function declaration to program root
 ERROR: rules/no-multi-spaces.ts[1, 22]: Multiple spaces found before 'true'.
 ERROR: rules/semicolon.ts[1, 24]: Unnecessary semicolon

tslint.js

@@ -52,6 +52,7 @@ module.exports = {
     'no-reference-import': true,
     'no-switch-case-fall-through': true,
     'no-unused-expression': [true, 'allow-fast-null-checks', 'allow-tagged-template'],
+    'no-unused-variable': [true, { 'ignore-pattern': '^_' }],
     'no-use-before-declare': true,
     'no-var-keyword': true,
     'radix': true,