Add a metadata control option

[jidanni]

Here we see with multiple -f's the metadata is simply combined.

  <metadata>
    <name>2019-10-14_04-54-442019-10-14_05-01-552019-10-14_05-05-002019-10-14_05-52-10</name>
    <link href="https://greentracks.app/">
      <text>GTs(Green Tracks)</text>
    </link>
    <link href="https://greentracks.app/">
      <text>GTs(Green Tracks)</text>
    </link>
    <link href="https://greentracks.app/">
      <text>GTs(Green Tracks)</text>
    </link>
    <link href="https://greentracks.app/">
      <text>GTs(Green Tracks)</text>
    </link>
    <time>2019-10-23T20:46:01.006Z</time>
    <bounds minlat="24.167679000" minlon="120.863075000" maxlat="24.179916000" maxlon="120.867200000"/>
  </metadata>

Please add a way to

• get rid of duplicate tags
• set a name other than ABCD all jammed together
• control the other tags there too (time, bounds...)