* Xls Reader Handle MACCENTRALEUROPE With or Without Hyphen
Fixes issue #549 and https://github.com/Maatwebsite/Laravel-Excel/issues/989 (which is the source of the new test file). Some systems accept MACCENTRALEUROPE as the name for the appropriate encoding, and some accept MAC-CENTRALEUROPE. I fortunately have access to at least one of each type, and have run the tests on each.
CodePage.php has an array of translations from codepage number to string. I now allow the value to itself be an array; if so, the code will test each in turn to see if it can be used in iconv. I did not go fishing for other similar problems. If such show up, they can be dealt with in the same manner as this one. I don't really expect others, since this is a problem not merely for Xls, but, even then, it applies only to BIFF5 and earlier.
I also moved XlsTest from Reader to Reader/Xls.
* Cache Successful Result For Future Use
Per suggestion from @MarkBaker
oleibman