Implement trap statement.

trap { 'trapped' }
trap { continue }
trap { break }
trap { $_.Exception.Message }
Implement trap with type constraint.

trap [System.FormatException] { }
Match trap type constraint with exception base type.

The following PowerShell now works:

    throw new-object System.FormatException

    trap [Exception] {
        'FormatException trapped'
        continue
    }
Merge pull request #163 from mrward/trap

Implement trap statement