Some sanity in file naming

[PaulMaddox]

When generating polymorphic/union types, do not name the file/struct by
joining the possible types. This lead to some horrific generated
filenames such as awsserverlessfunction_s3eventorsnseventorkinesiseventordynamodbeventorapieventorscheduleeventorcloudwatcheventeventoriotruleeventoralexaskillevent.go
(!!!). This broke compilation on Windows.

This change updates the generation to use the property name instead of it's possible types.

For example, this:

template := &cloudformation.Template{
    Resources: map[string]interface{}{
        "MySAMFunction": cloudformation.AWSServerlessFunction{
            Handler: "nodejs6.10",
            CodeUri: &cloudformation. AWSServerlessFunction_StringOrS3Location{
                String: &codeuri,
            },
        },
    },
}

Becomes this:

template := &cloudformation.Template{
    Resources: map[string]interface{}{
        "MySAMFunction": cloudformation.AWSServerlessFunction{
            Handler: "nodejs6.10",
            CodeUri: &cloudformation.AWSServerlessFunction_CodeUri{
                String: &codeuri,
            },
        },
    },
}

This fixes #37

[amnyulwa]

I'm still facing the same issue when doing the: go get github.com/awslabs/aws-sam-local

Error: go build github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/cloudformation: C:\Go\pkg\tool\windows_amd64\compile.exe: fork/exec C:\Go\pkg\tool\windows_amd64\compile.exe: The filename or extension is too long.

[rui-ktei]

I'm facing the same issue. Will there be a fix on this?