Structs for function input

Change the inputs for the two functions.

README.md

@@ -14,7 +14,7 @@ You can currently only create invoices and items in the invoices. For this purpo
 Here you will find an example how to create a new invoice in sevDesk.
 
 ```go
-invoice, err := sevdesk.NewInvoice(sevdesk.Invoice{323456, "21.11.2020", 100, "RE", 234353, "token"})
+invoice, err := sevdesk.NewInvoice(sevdesk.Invoice{"323456", "21.11.2020", "100", "RE", "234353", "token"})
 	if err != nil {
 		fmt.Println("Error: ", err)
 	}
@@ -33,7 +33,7 @@ For this I have worked it all out as follows. The funny thing is that the ID doe
 In sevDesk the price is transferred in gross, therefore we have added a calculation of the gross value to the function. So you set the net value + the VAT in the function.
 
 ```go
-Position, err := NewPosition(Position{45, 1, 16, "Backups", "Backups of all Websites", 9, invoiceID, "token"})
+Position, err := NewPosition(Position{"45", "1", "16", "Backups", "Backups of all Websites", "9", "invoiceID", "token"})
 	if err != nil {
 		fmt.Println("Error: ", err)
 	}

invoice.go

@@ -4,17 +4,16 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/url"
-	"strconv"
 	"strings"
 )
 
 // The data that the function uses
 type Invoice struct {
-	ContactID     int
+	ContactID     string
 	InvoiceDate   string
-	Status        int
+	Status        string
 	InvoiceType   string
-	ContactPerson int
+	ContactPerson string
 	Token         string
 }
 
@@ -109,17 +108,17 @@ func NewInvoice(config Invoice) (InvoiceReturn, error) {
 	// Define body data
 	body := url.Values{}
 	body.Set("invoiceNumber", "")
-	body.Set("contact[id]", strconv.Itoa(config.ContactID))
+	body.Set("contact[id]", config.ContactID)
 	body.Set("contact[objectName]", "Contact")
 	body.Set("invoiceDate", config.InvoiceDate)
 	body.Set("header", "")
-	body.Set("status", strconv.Itoa(config.Status))
+	body.Set("status", config.Status)
 	body.Set("invoiceType", config.InvoiceType)
 	body.Set("currency", "EUR")
 	body.Set("mapAll", "true")
 	body.Set("objectName", "Invoice")
 	body.Set("discount", "false")
-	body.Set("contactPerson[id]", strconv.Itoa(config.ContactPerson))
+	body.Set("contactPerson[id]", config.ContactPerson)
 	body.Set("contactPerson[objectName]", "SevUser")
 	body.Set("taxType", "default")
 	body.Set("taxRate", "")

position.go

@@ -10,13 +10,13 @@ import (
 )
 
 type Position struct {
-	PriceNet    float64
-	Quantity    float64
-	TaxRate     int
+	PriceNet    string
+	Quantity    string
+	TaxRate     string
 	Name        string
 	Description string
-	UnityID     int
-	InvoiceID   int
+	UnityID     string
+	InvoiceID   string
 	Token       string
 }
 
@@ -134,24 +134,36 @@ type InvoicePositionObjects struct {
 // To create new
 func NewPosition(config Position) (PositionReturn, error) {
 
-	// Calc to gross
-	gross := config.PriceNet + (config.PriceNet * float64(config.TaxRate) / 100)
+	// Convert string to float64
+	priceNet, err := strconv.ParseFloat(config.PriceNet, 64)
+	if err != nil {
+		return PositionReturn{}, err
+	}
+
+	// Convert taxRate from string to float64
+	taxRate, err := strconv.ParseFloat(config.TaxRate, 64)
+	if err != nil {
+		return PositionReturn{}, err
+	}
+
+	// Calc gross
+	priceGross := priceNet + (priceNet * taxRate / 100)
 
 	// Define client
 	client := &http.Client{}
 
 	// Define body data
 	body := url.Values{}
-	body.Set("price", fmt.Sprintf("%.2f", gross))
-	body.Set("quantity", fmt.Sprintf("%.2f", config.Quantity))
-	body.Set("taxRate", strconv.Itoa(config.TaxRate))
+	body.Set("price", fmt.Sprintf("%.2f", priceGross))
+	body.Set("quantity", config.Quantity)
+	body.Set("taxRate", config.TaxRate)
 	body.Set("name", config.Name)
 	body.Set("text", config.Description)
-	body.Set("unity[id]", strconv.Itoa(config.UnityID))
+	body.Set("unity[id]", config.UnityID)
 	body.Set("unity[objectName]", "Unity")
 	body.Set("objectName", "InvoicePos")
 	body.Set("mapAll", "true")
-	body.Set("invoice[id]", strconv.Itoa(config.InvoiceID))
+	body.Set("invoice[id]", config.InvoiceID)
 	body.Set("invoice[objectName]", "Invoice")
 
 	// Define request