feat(eslint-plugin): add prefer-string-starts-ends-with rule (#289)

Fixes #285

packages/eslint-plugin/docs/rules/prefer-string-starts-ends-with.md

@@ -0,0 +1,54 @@
+# Enforce the use of `String#startsWith` and `String#endsWith` instead of other equivalent methods of checking substrings (prefer-string-starts-ends-with)
+
+There are multiple ways to verify if a string starts or ends with a specific string, such as `foo.indexOf('bar') === 0`.
+
+Since ES2015 has added `String#startsWith` and `String#endsWith`, this rule reports other ways to be consistent.
+
+## Rule Details
+
+This rule is aimed at enforcing a consistent way to check whether a string starts or ends with a specific string.
+
+Examples of **incorrect** code for this rule:
+
+```ts
+let foo: string;
+
+// starts with
+foo[0] === 'b';
+foo.charAt(0) === 'b';
+foo.indexOf('bar') === 0;
+foo.slice(0, 3) === 'bar';
+foo.substring(0, 3) === 'bar';
+foo.match(/^bar/) != null;
+/^bar/.test(foo);
+
+// ends with
+foo[foo.length - 1] === 'b';
+foo.charAt(foo.length - 1) === 'b';
+foo.lastIndexOf('bar') === foo.length - 3;
+foo.slice(-3) === 'bar';
+foo.substring(foo.length - 3) === 'bar';
+foo.match(/bar$/) != null;
+/bar$/.test(foo);
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+foo.startsWith('bar');
+foo.endsWith('bar');
+```
+
+## Options
+
+There are no options.
+
+```JSON
+{
+    "@typescript-eslint/prefer-string-starts-ends-with": "error"
+}
+```
+
+## When Not To Use It
+
+If you don't mind that style, you can turn this rule off safely.