Added getline.cs to project.
Modified getline.cs to work with already written prompt, integrated it in user interface of Pash, made optional with variable.
Added new file for testing the ui.
Added unit tests for user interface that work with limitations

The unit tests work with the nunit IDE plugin. However, with nunit-console and nunit-gui they
do not work, as Console.SetIn() doesn't work as intended. Instead it's waiting for user input.

The second limitation is that running these tests with nunit will never test the getline-based ui.
This is because nunit doesn't run in a terminal emulator and thus properties like Console.WindowWidth
are 0, so getline.cs isn't usable.

I hope that some of the limitations can be overcome in the future, s.t. more unit tests can be added.
Merge pull request #170 from sburnicki/getline_integration_take2

Getline Integration - Take 2