Simple Todo v1.9.0

As requested in #12. Simple todo v1.9.0 now support overriding actions!🥳🥳
These can be configured in the settings.json and would look something like this:

"simpleTodo.overrideActionKeywords": [
    {
      "actionName": "Todo:",
      "severity": "Information"
    },
    {
      "actionName": "Bug:",
      "severity": "Warning"
    },
    {
      "actionName": "Fix:",
      "severity": "Information"
    },
    {
      "actionName": "Note:",
      "severity": "Hint"
    }
]

Note that the actions names and severity levels are not case sensitive.