Removed EnableLegacyExpectations switch

Actual legacy expectations functionality was removed back in commit cdcb7d6 , but the switch parameter was still defined on the Invoke-Pester command.
Rolling back some earlier Pester Scope changes

Per discussions with @nohwnd, the idea of having "It" be its own Pester scope (clearing Mocks and TestDrive contents the same way Context and Describe do) feels a bit awkward in practice.  We're starting to roll back those changes until we find the right balance; for now, Mocks are still affected by It scopes, but TestDrive has reverted back to Pester 2.0 behavior (only rolling back TestDrive contents when exiting a Context or Describe block.)

Also, default behavior of Assert-MockCalled has changed to be more in line with Pester 2.0 behavior, possibly allowing old test scripts to function without any modifications.  The default value for the Scope parameter is now either Context or Describe, depending on whether there is a currently-active Context block.  You can still pass in -Scope <Describe | Context | It> to override this behavior, if desired.

Tests of these bits have been updated to match the new behavior.  Possibly more changes coming along these lines, once we've tested this revision a bit.
Invoke-Pester tests path fix.

At some point while working on the early 3.0 beta code, we changed from executing *.Tests.ps1 with Invoke-Pester to just *Tests.ps1 .  I'm not sure why this was done, but it represents an unnecessary breaking change (and a bug, considering that New-Fixture still assumes that tests file will end in ".Tests.ps1", and the script under test will be named identically without the ".Tests" portion.)

Reverted this filter back to "*.Tests.ps1".
Merge pull request #164 from dlwyatt/ScopeBehaviorChanges

Rolling back some earlier Pester Scope changes
Merge pull request #165 from dlwyatt/LegacyExpectationsCleanup

Legacy expectations cleanup
Merge pull request #166 from dlwyatt/TestPathFix

Invoke-Pester tests path fix.
Changelog for previous changes
Fix formatting