Squashed 'posh-git/' content from commit 3874a02

git-subtree-dir: posh-git
git-subtree-split: 3874a02de8ce2b7d4908a8c0cb302294358b972c
Merge commit 'e5c92c4221a4d29c5de0ab477535d525f5086ec1' as 'posh-git'
moving powershell modules to dedicated powershell subdirectory