REPL sessions

[drewburlingame]

PoC: #306

Add a middleware feature to support REPL sessions. Execute commands within a REPL session. CommandContext state must remain isolated between commands. ReadLine functionality within the session, such as navigating & editing the input line and also scrolling history within the session.

Stretch goals: support piping | to other commands within the app & piping to/from file using > & <

[drewburlingame]

PoC @ #306 using https://github.com/tonerdo/readline This will be updated to use the CommandDotNet ReadLine from #315

[drewburlingame]

updated PoC @ #402 with package at https://www.nuget.org/packages/CommandDotNet/6.1.0-alpha.repl