Add AppVeyor config

AppVeyor provides a free Windows-based CI environment, which allows
native Windows LOOT builds to be automated!

scripts/appveyor/install_boost.ps1

@@ -0,0 +1,46 @@
+Add-Type -AssemblyName System.IO.Compression.FileSystem
+
+$boostUrl = 'http://downloads.sourceforge.net/project/boost/boost/1.61.0/boost_1_61_0.7z?r=https%3A%2F%2Fsourceforge.net%2Fprojects%2Fboost%2Ffiles%2Fboost%2F1.61.0%2F&ts=1468862599&use_mirror=ncu'
+$boostArchive = 'C:\projects\boost_1_61_0.7z'
+$boostFolder = 'C:\projects\boost_1_61_0'
+$boostLibraries = @(
+  'libboost_atomic-vc140-mt-s-1_61.lib'
+  'libboost_chrono-vc140-mt-s-1_61.lib'
+  'libboost_date_time-vc140-mt-s-1_61.lib'
+  'libboost_filesystem-vc140-mt-s-1_61.lib'
+  'libboost_iostreams-vc140-mt-s-1_61.lib'
+  'libboost_locale-vc140-mt-s-1_61.lib'
+  'libboost_log_setup-vc140-mt-s-1_61.lib'
+  'libboost_log-vc140-mt-s-1_61.lib'
+  'libboost_regex-vc140-mt-s-1_61.lib'
+  'libboost_system-vc140-mt-s-1_61.lib'
+  'libboost_thread-vc140-mt-s-1_61.lib'
+)
+
+function Is-LibraryMissing {
+  $libFolder = $boostFolder + '\stage\lib'
+  foreach($library in $boostLibraries) {
+    if (!(Test-Path ($libFolder + '\' + $library))) {
+      return $true
+    }
+  }
+
+  return $false
+}
+
+if (Is-LibraryMissing) {
+  Write-Output 'Downloading Boost 1.61.0...'
+
+  $start_time = Get-Date
+  (New-Object System.Net.WebClient).DownloadFile($boostUrl, $boostArchive)
+
+  Write-Output "Time taken: $((Get-Date).Subtract($start_time).Seconds) second(s)"
+
+  Write-Output 'Extracting ' + $boostArchive + '...'
+  cd 
+  7z x $boostArchive -o"C:\projects"
+
+  cd $boostFolder
+  .\bootstrap.bat
+  .\b2 toolset=msvc threadapi=win32 link=static runtime-link=static variant=release address-model=32 --with-log --with-date_time --with-thread --with-filesystem --with-locale --with-regex --with-system  --with-iostreams
+}