We now always trust the file extension to avoid false positive of mime
detection for most simple cases. But we still try to guess the mime type
if the file extension does not match or is missing.
Fixes#564
CSV reader used to accept any file without any kind of check. That made
users incorrectly believe that things were ok, even though there is no
way for CSV reader to read anything else that plain text files.
Fixes#167
Because even if it doesn't make a difference in practice, it is
technically more correct to call static methods statically. It
also better advertise that those methods can be used from any context.
Removed "unescape enclosure functionality", since the unescaping is already handled by fgetcsv,
and performing the unescaping again would actually result int the text from the cell being read wrong.
As an example try parsing the folowing CSV:
```
"<img alt="""" src=""http://example.com/image.jpg"" />"
```
With the additional unescaping it would have ended up as:
```
<img alt=" src="http://example.com/image.jpg" />
```
instead of the correct:
```
<img alt="" src="http://example.com/image.jpg" />
```
Fixes https://github.com/PHPOffice/PHPExcel/pull/1171
Laurent
