Add new case: int_gte && int_lte && regard enum as integer

[Tang-RoseChild]

i add some new cases for integer:
int_gte : equal or greater than
int_lte : equal or smaller than

and another case :
regard enum as interger. 'cause enum in pb files is still an integer, as follow:

type GetTimelineReq_Type int32

const (
	GetTimelineReq_ALL   GetTimelineReq_Type = 0
	GetTimelineReq_USER  GetTimelineReq_Type = 1
	GetTimelineReq_TOPIC GetTimelineReq_Type = 2
)

this is part of golang pb file

and my pull request is :
https://github.com/mwitkow/go-proto-validators/pull/22/files