Per language HOWTO's on writing functions (#208)

* fnctl: improve UX for howto's

* doc: go function howto

* fnctl: show the progress of build calls

* doc: php function howto

* doc: fix Go HOWTO

* doc: Node Functions HOWTO

* doc: Python Functions HOWTO

* doc: improve README files

* doc: ccirello -> USERNAME

* docs: fix Python example

Used an idiomatic method (isatty) to decide whether stdin must
be read or not.

* doc: fix go example

* fnctl: fix docker push output

docs/howto/go/.gitignore

@@ -0,0 +1,5 @@
+vendor/
+/hello
+/go
+/app
+/__uberscript__

docs/howto/go/Dockerfile

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+FROM iron/go
+
+WORKDIR /app
+ADD . /app
+
+ENTRYPOINT ["./hello"]

docs/howto/go/README.md

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+## Quick Example for a Go Function (3 minutes)
+
+This example will show you how to test and deploy Go (Golang) code to IronFunctions.
+
+### 1. Prepare the `functions.yaml` file:
+
+At functions.yaml you will find:
+```yml
+app: goapp
+route: /hello
+image: USERNAME/hello:0.0.1
+build:
+- docker run --rm -v "$PWD":/go/src/ -w /go/src/ -e "GOPATH=/go/src/vendor:/go" iron/go:dev go build -o hello
+```
+
+The important step here is to ensure you replace `USERNAME` with your Docker Hub account name. Some points of note:
+the application name is `goapp` and the route for incoming requests is `/hello`. These informations are relevant for
+the moment you try to test this function.
+
+### 2. Build:
+
+```sh
+fnctl publish
+```
+
+`-v` is optional, but it allows you to see how this function is being built.
+
+### 3. Queue jobs for your function
+
+Now you can start jobs on your function. Let's quickly queue up a job to try it out.
+
+```sh
+cat hello.payload.json | fnctl run goapp /hello
+```
+
+Here's a curl example to show how easy it is to do in any language:
+
+```sh
+curl -H "Content-Type: application/json" -X POST -d @hello.payload.json http://localhost:8080/r/goapp/hello
+```

docs/howto/go/functions.yaml

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+app: goapp
+route: /hello
+image: USERNAME/hello:0.0.1
+build:
+- docker run --rm -v "$PWD":/go/src/ -w /go/src/ -e "GOPATH=/go/src/vendor:/go" iron/go:dev go build -o hello

docs/howto/go/hello.go

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+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+type Person struct {
+	Name string
+}
+
+func main() {
+	p := &Person{Name: "World"}
+	json.NewDecoder(os.Stdin).Decode(p)
+	fmt.Println("Hello", p.Name, "!!!")
+}

docs/howto/go/hello.payload.json

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+{
+    "name": "Johnny"
+}