fix code example

Code example references a direct call to `Error` which fails, proper example should us the `binding.Error` instead.
return `Content-Type: application/json` in `ErrorHandler

The `ErrorHandler` defaults to returning `text/plain` despite the fact that it actually returns JSON. I've set the `Content-Type` header to `application/json; charset=utf-8`.
Merge pull request #52 from danawoodman/patch-2

fix code example
Merge pull request #53 from danawoodman/patch-3

return `Content-Type: application/json` in `ErrorHandler
JMS #55: Added support for removing a session key

closes #55
Merge branch 'JMS-55'
Merge branch 'master' of github.com:savruk/martini-contrib into savruk-master
Cleaned up Delims docs. Formatting
Changed Delim to Delims
Updated readme
Added nested required fields support

Modified the binding.Validate to recurse into required fields that are
structs.

given the Scenario:
  User struct {
          Name string  `json:"name" required`
          Home Address `json:"address" required`
  }

  Address struct {
          Street1 string `json:"street1" required`
          Street2 string `json:"street2"`
  }

I would expect Validation to fail unless street1 is specified.
However, the existing validation only checked using DeepEquals, which
looks for overall differences between the zero value and the actual.

To resolve the issue, Validate now checks the Kind of each required
field, and recurses into the value if it is a struct.
added wercker.yml
Merge pull request #59 from superlogical/master

added wercker.yml
Update README.md
Merge pull request #58 from egravert/nested_required

[binding] Added nested required fields support
[binding] Made “required” indicator syntax conventional; closes #60.