add OEPS/OEP-68.md

OEPS/OEP-68.md

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+```
+  OEP: X
+  Title: Streaming Payment Standard
+  Author: laizy <[email protected]>
+  Type: Draft
+  Status: XXX
+  Created: 2020-04-16
+```
+
+## Abstract
+
+This standard allows for the implementation of a standard API for streaming payment within smart contracts.
+
+
+## Motivation
+
+A standard interface which allows continuous token payment during a time range on the Ontology blockchain.
+
+## Specification
+
+### Structs
+the Stream struct is defined as follows:
+
+```go
+type Stream struct {
+  From      Address  // the payer
+  To        Address  // the receiver
+  Amount    uint128  // the total money to be streamed 
+  Token     Address  // the token address to be streamed
+  StartTime uint128  // the unix timestamp for when the stream starts
+  StopTime  uint128  // the unix timestamp for when the stream stops
+}
+```
+
+### Basic Methods
+
+#### createStream
+```go
+func createStream(from, to Address, amount uint128, token Address, 
+  startTime, stopTime uint128) (streamId uint128)
+```
+
+Create a new stream:
+1. check witness of `from`;
+2. check `to != zero && to != from && to != currentContractAddress`;
+3. check `CurrentBlockTime <= startTime < stopTime`;
+4. transfer token from `from` to this contract.
+
+#### balanceOf
+
+```go
+func balanceOf(streamId uint128, addr Address) (balance uint128)
+```
+Returns the current balance of the `addr` account.
+
+#### getStream
+
+```go
+func getStream(uint128 streamId) (
+    from, to Address, amount uint128,
+    token Address,  startTime, stopTime uint128,
+    uint128 remainingBalance, uint128 ratePerSecond
+)
+```
+Returns the current active stream infomation.
+
+#### withdrawFromStream
+
+```go
+func withdrawFromStream(streamId uint128) returns (uint128);
+```
+
+Transfer the streamed token to `To` address, can be called by `To` or `Proxy`, return amount transfered 
+
+#### cancelStream
+
+```go
+func cancelStream(streamId uint128) (bool);
+```
+
+Cancel the stream, can be called by `From` or `To` address.
+
+### Optional Methods
+
+#### setProxy
+
+```go
+func setProxy(addr Address)
+```
+
+Set the proxy, which can be used to call the `withdrawFromStream`. this function should be called by contract Admin.
+
+### Events
+
+#### createStream
+
+```
+event createStream(streamId uint128, from, to Address, amount uint128,
+  token Address, startTime, stopTime uint128);
+```
+
+Triggered when a stream is created.
+
+#### withdrawFromStream
+
+```
+event withdrawFromStream(streamId uint128, to Address, amount uint128);
+```
+Triggered when a withdrawFromStream method is called successfully.
+
+#### cancelStream
+
+```
+event cancelStream(streamId uint128, from, to Address, 
+     fromBalance, toBalance uint128);
+```
+
+Triggered when a cancelStream method is called successfully.
+
+### Implementation
+