update doc and move App and Session to standalone files.

README.md

@@ -0,0 +1,54 @@
+A Facebook Graph API Library In Go
+=================================
+
+This is a Go library supports Facebook Graph API and FQL. It's simple but powerful.
+
+Quick Tutorial
+---------------
+
+```go
+  import (
+      "fmt"
+      fb "github.com/huandu/facebook"
+  )
+
+  func main() {
+      res, _ := fb.Get("/538744468", fb.Params{
+          "fields": "username",
+      })
+      fmt.Println("here is my facebook username:", res["username"])
+
+      // It's easy to decode "username" to a go string too.
+      var username string
+      res.DecodeField("username", &username)
+      fmt.Println("alternative way to get username:", username)
+
+      // It's also possible to decode the whole result into a predefined struct.
+      // Assume the struct is defined as following:
+      //     type User struct {
+      //         Username string
+      //     }
+      //
+      // Then, you can use following code to fill struct with values in result.
+      //     var user User
+      //     res.Decode(&user)
+  }
+```
+
+For more document, please read http://godoc.org/github.com/huandu/facebook or use `go doc`.
+
+Get It
+------
+
+Use `go get github.com/huandu/facebook` to get and install it.
+
+Out of Scope
+------------
+
+1. No OAuth integration.
+2. No old RESTful API support.
+
+License
+-------
+
+This library is licensed under MIT license.