DesiredCapabilities + WebDriverPlatform

Make desired capabilities object-oriented. To start a RemoteWebDriver
instance, we can use pre-defineded DesiredCapabilities instead of
constructing an array everytime.

For example, to start Chrome.
```
$driver = RemoteWebDriver::create($url, DesiredCapabilities::chrome());
```
Update README.md

Migrate to DesiredCapabilities.
ChromeOptions - setBinary, addExtensions
typo extension vs extensions
phpdoc for ChromeOptions
allow empty chrome options
Merge branch 'develop' of github.com:komex/php-webdriver into komex-develop
merge
ChromeOptions: setExperimentalOptions, addArguments

Start Chrome with arguments.

Example,
```
$options = new ChromeOptions();
$options->addArguments(array('--window-size=300,900'));
$caps = DesiredCapabilities::chrome();
$caps->setCapability(ChromeOptions::CAPABILITY, $options);
$driver = RemoteWebDriver::create($url, $caps);
```
DriverCommand
Update README.md
Standardize WebDriver Response
fix
update test
Update HttpCommandExecutor.php

Bugfix, as current code breaks execution with PHP 5.3 (unsupported language feature).
Merge branch 'TobiasLang-patch-1'