Changes

• Add koans for PSProviders. Currently includes FileSystem, Alias, Function, Variable and Environment providers, and different methods of using their contents. Registry has been omitted for the time being due to cross-platform concerns, as well as concerns over having folks just learning PoSH being given the keys to the Windows registry a little early.
• Add [Koan()] attributes to all koan files. These attributes take a single uint32 parameter that denotes their position in the order of tests.
• Add #Requires -Module PSKoans to all koan files. This should ensure that PowerShell automatically imports the PSKoans module (if you have it installed; will be more useful when we start uploading to the gallery), and gives a more helpful error message than 'missing attribute' if the KoanAttribute class is not loaded.
• Added logic to Get-Enlightenment which sorts the koan test files by their index numbers before feeding them to Invoke-Pester one at a time. Files with no attribute will be skipped entirely, whereas files with no set index number (in the format [Koan(1)], for example) will automatically receive an index of [uint32]::MaxValue and be 'last' in the list of koans to complete.