docs: Clean up structure

Closes #117.
Formatter: Checkstyle

Created checkstyle formatter based off of the example here: http://www.jshint.com/docs/config/

`eslint -f checkstyle foo.js` will not produce output that looks like this:

<?xml version="1.0" encoding="utf-8"?>
<checkstyle version="4.3">
	<file name="foo.js">
		<error line="5" column="10" severity="error" message="Unexpected foo." />
	</file>
</checkstyle>

Fixes #14
Rule to warn on use of Math and JSON as functions
Merge pull request #118 from iancmyers/formatter-checkstyle

Formatter: Checkstyle (fixes #14)
Merge pull request #100 from ilyavolodin/no-native-reassign

Rule: no native reassignment
Merge pull request #120 from jamesallardice/rule-no-obj-calls

Rule: Warn on use of Math and JSON as functions
Rebase against master branch
Fixes incorrect reporting of missing semicolon

This fixes the incorrect reporting of missing semicolons when there is no whitespace between the end of a statement and the next token. The semicolon is already included in the tokens returned by `getTokens`, so grabbing one more character after would just grab a whitespace character. In this case because whitespace was not present it grabbed the closing curly, saw that it wasn't a semicolon and reported it as an error.

`setTimeout(function() {foo = "bar";});`

Fixes #121
Merge pull request #125 from iancmyers/fix-semi

Fixes incorrect reporting of missing semicolon
Merge pull request #117 from mathiasbynens/fix-docs

docs: Clean up structure
Rule: Variables should not be deleted
Rebasing on master