feature: worksheet AddButton

[JDavidVR]

I've reviewed documentation, and there is no information about inserting a button to xlsx file

I did some research and here is a good example to have a buttom: https://xlsxwriter.readthedocs.io/example_macros.html

So these are my findings:

Buttons are added in this file: xl/drawings/vmlDrawing1.vml

<xml xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office"
     xmlns:x="urn:schemas-microsoft-com:office:excel">
    <o:shapelayout v:ext="edit">
        <o:idmap v:ext="edit" data="1"/>
    </o:shapelayout>
    <v:shapetype id="_x0000_t201" coordsize="21600,21600" o:spt="201" path="m,l,21600r21600,l21600,xe">
        <v:stroke joinstyle="miter"/>
        <v:path shadowok="f" o:extrusionok="f" strokeok="f" fillok="f" o:connecttype="rect"/>
        <o:lock v:ext="edit" shapetype="t"/>
    </v:shapetype>
    <v:shape id="_x0000_s1025" type="#_x0000_t201"
             style="position:absolute;margin-left:161.25pt;margin-top:30pt;width:60pt;height:22.5pt;z-index:1;mso-wrap-style:tight"
             o:button="t" fillcolor="buttonFace [67]" strokecolor="windowText [64]" o:insetmode="auto">
        <v:fill color2="buttonFace [67]" o:detectmouseclick="t"/>
        <o:lock v:ext="edit" rotation="t"/>
        <v:textbox style="mso-direction-alt:auto" o:singleclick="f">
            <div style="text-align:center">
                <font face="Calibri" size="220" color="#000000">Press Me</font>
            </div>
        </v:textbox>
        <x:ClientData ObjectType="Button">
            <x:Anchor>1, 0, 2, 0, 2, 16, 3, 10</x:Anchor>
            <x:PrintObject>False</x:PrintObject>
            <x:AutoFill>False</x:AutoFill>
            <x:FmlaMacro>[0]!say_hello</x:FmlaMacro>
            <x:TextHAlign>Center</x:TextHAlign>
            <x:TextVAlign>Center</x:TextVAlign>
        </x:ClientData>
    </v:shape>
</xml>

Values that are dynamics are those:

<v:shape id="_x0000_s1025"` dynamic

<v:shape style="
                margin-left:%.15gpt; dynamic
                margin-top:%.15gpt; dynamic
                width:%.15gpt; dynamic
                height:%.15gpt; dynamic
                z-index:%d; dynamic

<v:textbox>
                <div>
                                <font>Press Me</font> dynamic

<x:ClientData >
                <x:Anchor>1, 0, 2, 0, 2, 16, 3, 10</x:Anchor> dynamic
                <x:FmlaMacro>[0]!say_hello</x:FmlaMacro> dynamic

I can work on implementation but I need some guidelines, like if I should create a new go file called, button.go and a tamplate in templates.go