Fixing a mocking parameter bug

@Jaykul pointed out a problem where the $args variable in a mock's stub function can resolve to the value of $args in a parent scope; the automatic version of $args only exists for non-advanced functions.

The prototype function used to generate these stubs now looks specifically for a variable named args in the local scope, not allowing it to fetch the parent scope's values.
Merge pull request #187 from dlwyatt/MockFix

Fixing a mocking parameter bug
Update CHANGELOG.md
Better error messages when exported commands are called out of order

Most Pester commands are intended to be used inside a Describe block, and if you called them in other situations, you'd typically get many errors instead of a single terminating error at the start of a function.

This has been changed for all commands except for Invoke-Pester and New-Fixture (which are intended to be called outside of a running test).
Merge pull request #188 from dlwyatt/BetterErrorMessages

Better error messages when exported commands are called out of order
Update CHANGELOG.md