Ignore bin and obj folders

[angularsen]

Minor issue, but I had to remove all bin/obj folders before running the tool, or else it would fail with this.
Not sure if this is limited to just Xamarin Android/iOS projects or not, or if the problem is broader.

Alternatively, if finding out what folders to ignore is complicated since they can be customized, maybe this tool should not fail but rather log a warning for files it fails to parse.

Processing references for C:\dev\xxx\xxx\app\yyy.Android\obj\Debug\120\designtime\build.props...
Startup exception: System.Xml.XmlException: Data at the root level is invalid. Line 1, position 1.
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.Throw(String res, String arg)
   at System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace()
   at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.Linq.XDocument.Load(XmlReader reader, LoadOptions options)
   at System.Xml.Linq.XDocument.Load(String uri, LoadOptions options)
   at CentralisedPackageConverter.PackageConverter.ConvertProject(FileInfo csprojFile, Boolean dryRun) in /home/runner/work/CentralisedPackageConverter/CentralisedPackageConverter/CentralisedPackageConverter/PackageConverter.cs:line 228
   at CentralisedPackageConverter.PackageConverter.<>c__DisplayClass3_0.<ProcessConversion>b__5(FileInfo proj) in /home/runner/work/CentralisedPackageConverter/CentralisedPackageConverter/CentralisedPackageConverter/PackageConverter.cs:line 62
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at CentralisedPackageConverter.PackageConverter.ProcessConversion(String solutionFolder, Boolean revert, Boolean dryRun, Boolean force) in /home/runner/work/CentralisedPackageConverter/CentralisedPackageConverter/CentralisedPackageConverter/PackageConverter.cs:line 62
   at Program.<>c.<<Main>$>b__0_0(CommandLineOptions o) in /home/runner/work/CentralisedPackageConverter/CentralisedPackageConverter/CentralisedPackageConverter/Program.cs:line 10
   at CommandLine.ParserResultExtensions.WithParsed[T](ParserResult`1 result, Action`1 action)
   at Program.<Main>$(String[] args) in /home/runner/work/CentralisedPackageConverter/CentralisedPackageConverter/CentralisedPackageConverter/Program.cs:line 6

[BastianBirke]

My last PR #26: new DirectoryCrawler class, filtering by Regex: directories starting with dot, bin, obj.