Add detection for MacRoman encoding

MacRoman is not in particularly common use anymore, as it has been deprecated by Mac OS for over a decade. However, there are programs such as Microsoft Office for Mac that didn't get the memo, and will often output in MacRoman when they write plain text files.

This patch allows chardet to correctly detect MacRoman, instead of calling it something random and incorrect like ISO-8859-2. The MacRoman detector works similarly to the Latin-1 detector, but starts at a lower probability.

I hope this is the right way to do it. There is surprisingly little support in chardet for adding a new single-byte Latin encoding.