Add problemMatcher contribution
Add problemMatcher contribution

This adds a $valac problem matcher that can be used in tasks.

Example tasks.json:

    {
        "version": "0.1.0",
        "command": "valac",
        "isShellCommand": true,
        "args": [],
        "showOutput": "always",
        "problemMatcher": "$valac"
    }

thiagoabreu/vala-code