Appium W3C Implementation

* Appium 1.8.0 will be the first version of Appium to _fully_ implement [W3C](https://github.com/jlipps/simple-wd-spec)
* 1.7.2 accepts W3C parameters during session creation but coerces them into a MJSONWP session
* The [W3C](https://github.com/jlipps/simple-wd-spec) simplified spec doc that JLipps wrote explains most of how the spec works
* This document will elaborate on how Appium implements this spec

## Session Creation
* When parameters are passed to the session creation endpoint (`POST /session`), Appium will parse the body and determine if it should start a W3C or MJSONWP Session
  * If the body contains an object called `capabilities` it will be a W3C session
  * Else if the body contains an object called `desiredCapabilities` it will be an MJSONWP session
  * If both are provided, it will be a W3C session (NOTE: If anyone objects to this and feels that it should be MJSONWP, please let me know)
  * If w3c capabilities are provided, it will parse the caps as explained in the spec (https://github.com/jlipps/simple-wd-spec#processing-capabilities)
* Format of W3C capabilities object

  * Expected format is same as spec
  
```javascript
{
  capabilities: {
    alwaysMatch: {...},
    firstMatch: [{...}, ...}]
  }
}
```

  * Including MJSONWP and W3C is fine

  
```javascript
{
  desiredCapabilities: {...}
  capabilities: {
    alwaysMatch: {...},
    firstMatch: [{...}, ...}]
  }
}
```

  * 
  
### Session Creation Examples