Handle imports better and fix some bugs

Merge pull request dotnet#288 from cartermp/bump0.5

Bump to 0.5.x

Merge pull request dotnet#283 from cartermp/newver

Bump to 0.4

Merge pull request dotnet#280 from cartermp/no-web

Fail conversion if we see System.Web

Merge pull request dotnet#262 from jmarolf/feature/discover-supported…

…-tfms

Programatically determine highest tfm

Update dependencies from https://github.com/dotnet/arcade build 20200…

…107.5 (dotnet#189)

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20057.5
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.20057.5

nuget release 0.2.105701

Update dependencies from https://github.com/dotnet/arcade build 20191…

…021.4 (dotnet#106)

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19521.4
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.19521.4

Update dependencies from https://github.com/dotnet/arcade build 20191…

…010.4 (dotnet#96)

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19510.4
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.19510.4

Merge pull request dotnet#74 from jmarolf/bugfix/update-help-wording

try-convert