Add toggle for terminal and allow dot-sourcing for powershell.execute

[TylerLeonhardt]

This is a continuation of #73 by @mikeTWC1984

with some minor tweaks.

It adds the ability to toggle the integrated console with powershell.toggleTerminal and adds a new setting:

"powershell.integratedConsole.executeInCurrentScope"

which, when true (false is the default) will dot source a script in the session instead of letting it run in its own scope.

[TylerLeonhardt]

This also revs to version 0.1.0 to prep for a release. We can say this is little less alpha at this point :)