[WIP] Add cron-like job for periodic maintenance of settings db, update TODO.md

vendor/github.com/carlescere/scheduler/README.md

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+# scheduler
+[![GoDoc](https://godoc.org/github.com/carlescere/scheduler?status.svg)](https://godoc.org/github.com/carlescere/scheduler)
+[![Build Status](https://travis-ci.org/carlescere/scheduler.svg?branch=master)](https://travis-ci.org/carlescere/scheduler)
+[![Coverage Status](https://coveralls.io/repos/carlescere/scheduler/badge.svg?branch=master)](https://coveralls.io/r/carlescere/scheduler?branch=master)
+
+Job scheduling made easy.
+
+Scheduler allows you to schedule recurrent jobs with an easy-to-read syntax.
+
+Inspired by the article **[Rethinking Cron](http://adam.heroku.com/past/2010/4/13/rethinking_cron/)** and the **[schedule](https://github.com/dbader/schedule)** python module.
+
+## How to use?
+```go
+package main
+
+import (
+	"fmt"
+	"runtime"
+	"time"
+
+	"github.com/carlescere/scheduler"
+)
+
+func main() {
+	job := func() {
+		t := time.Now()
+		fmt.Println("Time's up! @", t.UTC())
+	}
+      // Run every 2 seconds but not now.
+	scheduler.Every(2).Seconds().NotImmediately().Run(job)
+      
+      // Run now and every X.
+	scheduler.Every(5).Minutes().Run(job)
+	scheduler.Every().Day().Run(job)
+	scheduler.Every().Monday().At("08:30").Run(job)
+      
+      // Keep the program from not exiting.
+	runtime.Goexit()
+}
+```
+
+## How it works?
+By specifying the chain of calls, a `Job` struct is instantiated and a goroutine is starts observing the `Job`.
+
+The goroutine will be on pause until:
+* The next run scheduled is due. This will cause to execute the job.
+* The `SkipWait` channel is activated. This will cause to execute the job.
+* The `Quit` channel is activated. This will cause to finish the job.
+
+## Not immediate recurrent jobs
+By default the behaviour of the recurrent jobs (Every(N) seconds, minutes, hours) is to start executing the job right away and then wait the required amount of time. By calling specifically `.NotImmediately()` you can override that behaviour and not execute it directly when the function `Run()` is called.
+
+```go
+scheduler.Every(5).Minutes().NotImmediately().Run(job)
+```
+
+## License
+Distributed under MIT license. See `LICENSE` for more information.