Increment assembly version

Incremented assembly version

Removed .NET Framework 4.5 and 4.6.1 target frameworks

Increment version to 4.4.1

Merge branch 'master' of https://github.com/neilharvey/FileSignatures

Update appveyor config

Remove nullable from benchmark test

Incremented package version

Increment package version to 4.1 #38

Update OpenMcdf to latest version. Fixes #37