[syslinux] support ISOs that use boot.bin instead of isolinux.bin

* Such as WebConverger (webc-35.1.iso)
* Also fix non installation of Syslinux if Alt-E (dual UEFI/BIOS) is set
* Also update README and AppVeyor script

appveyor.yml

@@ -2,12 +2,9 @@ os: Visual Studio 2015
 
 init:
   - ps: >-
-      if ($env:appveyor_repo_tag -eq "true")
-      {
+      if ($env:appveyor_repo_tag -eq "true") {
         Update-AppveyorBuild -Version "$env:appveyor_repo_tag_name"
-      }
-      else
-      {
+      } else {
         Update-AppveyorBuild -Version "dev-$($env:appveyor_repo_commit.substring(0,7))"
       }