Direct test execution fix

Corrects a bug that occurs when a test script is dot-sourced into the global scope.  In that situation, mocks can wind up being executed by modules that were not intended to see the mock (including Pester itself.)
Merge branch 'dlwyatt-GlobalMockFix' into Beta
ParameterFilter fixes

The script block passed to the -ParameterFilter parameters on Mock and Assert-MockCalled is now executed in the test script's scope.  To prevent errors when the parameter filter is being evaluated in some cases, Strict Mode is disabled within that block (but left alone otherwise).s
Merge branch 'dlwyatt-ParameterFilterFixes' into Beta
Adding Coverage Analysis (first pass)

Uses the AST to identify all commands in whatever script files the caller specifies, and sets empty PSBreakpoints on each of those commands.  After the tests finish, the breakpoints' HitCount properties are checked to determine coverage, and a report of any commands that have 0 HitCount is displayed.

Seems to work so far, but the tricky part is using this to analyze Pester's own test suite.  I've added several calls to Suspend-CoverageAnalysis and Resume-CoverageAnalysis (which basically correspond to Disable-PSBreakpoint and Enable-PSBreakpoint) to try to keep the number of false positives to a minimum, but I don't think we're ever going to be 100% accurate for our own internal tests.
Backtracking...

Performance hit was pretty deadly when I ran Pester's own tests using this feature.  Repeatedly disabling and enabling nearly 900 breakpoints brings the speed to its knees, and this performance hit would have been passed on to the users who weren't even affected by the problems of having Pester test itself.

However, I did get a single report run against Pester before I changed the code back, and it reported around 50% code coverage.  Definitely some room for improvement there.  I'll try to come up with a way to do a useful coverage analysis without a bunch of false positives against Pester in the future (maybe having two copies of the module with different prefixes, or something.  One to run the tests, the other to be analyzed for coverage.)