Add fill_template.ps1 for Powershell (#153)

This is a direct 1 to 1 version of existing fill_template script, but
for Powershell, to help developers using Windows.

fill_template.ps1

@@ -0,0 +1,13 @@
+$crate = Read-Host "To fill the template, tell me your egui project crate name: "
+$name = Read-Host "To fill the template, tell me your name (for author in Cargo.toml): "
+$email = Read-Host "To fill the template, tell me your e-mail address (also for Cargo.toml): "
+
+Write-Host "Patching files..."
+
+(Get-Content "Cargo.toml") -replace "eframe_template", $crate | Set-Content "Cargo.toml"
+(Get-Content "src\main.rs") -replace "eframe_template", $crate | Set-Content "src\main.rs"
+(Get-Content "index.html") -replace "eframe template", $crate -replace "eframe_template", $crate | Set-Content "index.html"
+(Get-Content "assets\sw.js") -replace "eframe_template", $crate | Set-Content "assets\sw.js"
+(Get-Content "Cargo.toml") -replace "Emil Ernerfeldt", $name -replace "emil.ernerfeldt@gmail.com", $email | Set-Content "Cargo.toml"
+
+Write-Host "Done."