Docs: Fixed NDK download links for Windows

<?cs

set:ndk.mac64_download='android-ndk-r12-darwin-x86_64.zip' ?><?cs

set:ndk.mac64_bytes='734014148' ?><?cs

set:ndk.mac64_checksum='708d4025142924f7097a9f44edf0a35965706737' ?><?cs

set:ndk.mac64_download='android-ndk-r12b-darwin-x86_64.zip' ?><?cs

set:ndk.mac64_bytes='734135279' ?><?cs

set:ndk.mac64_checksum='e257fe12f8947be9f79c10c3fffe87fb9406118a' ?><?cs

set:ndk.linux64_download='android-ndk-r12-linux-x86_64.zip' ?><?cs

set:ndk.linux64_bytes='755431993' ?><?cs

set:ndk.linux64_checksum='b7e02dc733692447366a2002ad17e87714528b39' ?><?cs

set:ndk.linux64_download='android-ndk-r12b-linux-x86_64.zip' ?><?cs

set:ndk.linux64_bytes='755551010' ?><?cs

set:ndk.linux64_checksum='170a119bfa0f0ce5dc932405eaa3a7cc61b27694' ?><?cs

set:ndk.win32_download='android-ndk-r12-windows-x86.zip' ?><?cs

set:ndk.win32_bytes='706332762' ?><?cs

set:ndk.win32_checksum='37fcd7acf6012d0068a57c1524edf24b0fef69c9' ?><?cs

set:ndk.win32_download='android-ndk-r12b-windows-x86.zip' ?><?cs

set:ndk.win32_bytes='706453972' ?><?cs

set:ndk.win32_checksum='8e6eef0091dac2f3c7a1ecbb7070d4fa22212c04' ?><?cs

set:ndk.win64_download='android-ndk-r12-windows-x86_64.zip' ?><?cs

set:ndk.win64_bytes='749444245' ?><?cs

set:ndk.win64_checksum='80d64a77aab52df867ac55cec1e976663dd3326f'

set:ndk.win64_download='android-ndk-r12b-windows-x86_64.zip' ?><?cs

set:ndk.win64_bytes='749567353' ?><?cs

set:ndk.win64_checksum='337746d8579a1c65e8a69bf9cbdc9849bcacf7f5'

?>

<?cs

def:size_in_mb(bytes)