add and modifier

add rnren.go:
+it is a client to access renren.com,listen on localhost:8080

mod oauth/oauth.go:
+add Avatars struct to storage avatar information
+add User struct to storage user info
+add User struct type to to the b struct value in the updateToken
func,means to get user information frome the json
+add User struct type to the Token struct,means to get the info outside
the package.And can write/read with the CacheFile

bugs:
+first time run the pro,some error with http will accur.do not know
why.but it will not effect the proeccs
delelte my client_id and client_secret