Add custom loader for Powershell, improve its implementation in Cmder

Fixes #104, fixes #53, fixes #65 (my bad), related to #136, and should
fix #139

vendor/profile.ps1

@@ -0,0 +1,39 @@
+# Global modules directory
+$global:PsGetDestinationModulePath = $PSScriptRoot + "\..\vendor\psmodules"
+
+# Push to modules location
+Push-Location -Path ($PsGetDestinationModulePath)
+
+# Load modules from current directory
+Get-ChildItem -Directory | `
+Foreach-Object{
+    Import-Module .\$_\$_
+}
+
+# Come back to PWD
+Pop-Location
+
+# Set up a Cmder prompt, adding the git prompt parts inside git repos
+function global:prompt {
+    $realLASTEXITCODE = $LASTEXITCODE
+    $Host.UI.RawUI.ForegroundColor = "white"
+    Write-Host($pwd.ProviderPath) -NoNewLine -ForegroundColor "green"
+    if (Get-Module posh-git) {
+        Write-VcsStatus
+    }
+    $global:LASTEXITCODE = $realLASTEXITCODE
+    return "`nλ "
+}
+
+# Load special features come from posh-git
+if (Get-Module posh-git) {
+    Enable-GitColors
+    Start-SshAgent -Quiet
+}
+
+# Move to the wanted location
+if (Test-Path Env:\CMDER_START) {
+    Set-Location -Path $Env:CMDER_START
+} elseif ($Env:CMDER_ROOT -and $Env:CMDER_ROOT.StartsWith($pwd)) {
+    Set-Location -Path $Env:USERPROFILE
+}