Parallelisation when scanning

[bjompen]

Today the folder scanning is serial, and matches one pattern / time. This could probably be greatly improved without impacting memory / cpu / disk usage by

• Build a list of files to scan
• Parallelise the pattern scans to perform ~5 simultaneous scans (configurable)
  • Preferably without loosing PowerShell 5.1 support..
• Replace PowerShell commands (Get-ChildItem, Get- Content, Select-String) with .net methods where possible.

All increases of speed are good and needed if this should be usable in plugins (#8 #9)