Ensure querystring is copied over for the function

[MarcusNoble]

Description

Fixes #25
Make the QueryString available within function.

How Has This Been Tested?

Manually tested against the following function:

package function

import (
	"github.com/openfaas-incubator/go-function-sdk"
)

// Handle a function invocation
func Handle(req handler.Request) (handler.Response, error) {
	return handler.Response{
		Body:       []byte(req.QueryString),
		StatusCode: http.StatusOK,
	}, err
}

How are existing users impacted? What migration steps/scripts do we need?

Checklist:

I have:

• updated the documentation and/or roadmap (if required)
• read the CONTRIBUTION guide
• signed-off my commits with git commit -s
• added unit tests

[viveksyngh]

This changes looks good to be me and I tried running in my local it worked fine.

But I think one change is very necessary in every template handler.go file to alias github.com/openfaas-incubator/go-function-sdk as handler. Because we are using that alias but it is not there.

[alexellis]

Vivek, thank you for the review I will now merge.

[alexellis]

Please feel free to raise an issue to cover your suggestion.

Marcus thanks very much too!

[viveksyngh]

I will raise the PR for that.

[viveksyngh]

LGTM