Add Start-PSBootstrap function

Installs Open PowerShell build dependenices on all platform; deprecates
`bootstrap.sh`.

PowerShellGitHubDev.psm1

@@ -261,6 +261,56 @@ function Start-PSxUnit {
     }
 }
 
+
+function Start-PSBootstrap {
+    [CmdletBinding()]param()
+
+    Write-Host "Installing Open PowerShell build dependencies"
+
+    if ($IsLinux) {
+        precheck 'curl' "Bootstrap dependency 'curl' not found in PATH, please install!" > $null
+        precheck 'apt-get' "Bootstrap dependency 'apt-get' not found in PATH, this only supports Ubuntu 14.04!" > $null
+
+        # Setup LLVM feed
+        curl -s http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
+        echo "deb http://llvm.org/apt/trusty/ llvm-toolchain-trusty-3.6 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+        sudo apt-get update -qq
+
+        # Install ours and .NET's dependencies
+        sudo apt-get install -y wget make g++ cmake libc6 libgcc1 libstdc++6 libcurl3 libgssapi-krb5-2 libicu52 liblldb-3.6 liblttng-ust0 libssl1.0.0 libunwind8 libuuid1 zlib1g clang-3.5
+
+        # Install .NET CLI packages
+        Remove-Item dotnet*.deb
+
+        wget https://dotnetcli.blob.core.windows.net/dotnet/beta/Installers/Latest/dotnet-host-ubuntu-x64.latest.deb
+        sudo dpkg -i dotnet-host-ubuntu-x64.latest.deb
+
+        wget https://dotnetcli.blob.core.windows.net/dotnet/beta/Installers/Latest/dotnet-sharedframework-ubuntu-x64.latest.deb
+        sudo dpkg -i dotnet-sharedframework-ubuntu-x64.latest.deb
+
+        wget https://dotnetcli.blob.core.windows.net/dotnet/beta/Installers/Latest/dotnet-sdk-ubuntu-x64.latest.deb
+        sudo dpkg -i dotnet-sdk-ubuntu-x64.latest.deb
+
+    } elseif ($IsOSX) {
+        precheck 'brew' "Bootstrap dependency 'brew' not found, must install Homebrew! See http://brew.sh/"
+
+        # Install ours and .NET's dependencies
+        brew install cmake wget openssl
+
+        # Install .NET CLI packages
+        Remove-Item dotnet*.pkg
+        wget https://dotnetcli.blob.core.windows.net/dotnet/beta/Installers/Latest/dotnet-dev-osx-x64.latest.pkg
+        sudo installer -pkg dotnet-dev-osx-x64.latest.pkg -target /
+    } elseif ($IsWindows -And -Not $IsCore) {
+        Invoke-WebRequest -Uri https://raw.githubusercontent.com/dotnet/cli/rel/1.0.0/scripts/obtain/install.ps1 -OutFile install.ps1
+        ./install.ps1
+        $env:Path += ";$env:LocalAppData\Microsoft\dotnet\cli"
+    } else {
+        Write-Warning "Start-PSBootstrap cannot be run in Core PowerShell on Windows (need Invoke-WebRequest!)"
+    }
+}
+
+
 function Start-PSPackage {
     [CmdletBinding()]param(
         # PowerShell packages use Semantic Versioning http://semver.org/