Fixed broken links (case sensitive)

> We should first explain exactly what we mean by "case sensitive URLs". Some Web servers (usually Unix servers) consider URLs to be case-sensitive. That is, they would treat each of the following URLs as referring to a different file:

 >     http://www.example.com/mypage.html
    http://www.example.com/MyPage.html
    http://www.example.com/MYPAGE.html
    http://www.example.com/MYPAGE.HTML

>If you visited `http://www.example.com/mypage.html` but the file was actually named "MyPage.html", these kinds of servers would display a "file not found" error.

> Other Web servers (mostly Windows servers) would treat all these URLs as requests for the same file, because they use a file system that doesn't care about capitalization. Using an incorrectly capitalized link on these kinds of servers doesn't cause an error.

> It's best to avoid this problem entirely by making sure that the capitalization of any URL links matches the capitalization of your file names, ensuring that your files work on any kind of server. However, if you have an existing site, these errors can be difficult to find.

Source: http://support.tigertech.net/case-sensitive

For example, GitHub runs a server of this type. As a result, the links fixed in this commit show the 404 error.

Also note that two UrlDownloadToFile html pages exist on ahkscript.org (<b>Url</b>DownloadToFile.htm and <b>URL</b>DownloadToFile.htm). The first one could be deleted if this pull request is merged.