Bumps dotnet-version to 6.0.x

 - fixes reading of cells with null char value yellowfeather#61

 - fixes handle null/empty string from BinaryReader.ReadString() yellowfeather#20 yellowfeather#112
 - fixes reading of negative currency values yellowfeather#62
 - fixes reading of number columns with length > 10 yellowfeather#33 yellowfeather#98
 - fixes reading character columns with length > 255 yellowfeather#67
 - sets the encoding from the language driver in the DBF file yellowfeather#131
 - targets net5.0
 - bumps dependencies

Bumps version to 0.7.0

Bumps version to 0.6.0

Bumps version to 0.5.8

Another update to artifacts path in appveyor.yml

Bumps version to 0.5.5

Bumps version to 0.5.6

Bumps version from 0.5.3 to 0.5.4

Reinstates MyGet API key (yellowfeather#53)