Deprecate `emphclass` about liblouis

[jrbowden]

Hi, I'm a bit concerned that some systems will need to guarantee the order of bits in the emphasis. UEB for example defines several additional classes of emphasis apart from italic, underline and bold. US defines different ones.
Do we guarantee that the bit order will be the same order as an emphasis class is defined in the table?

[bertfrees]

The bit order could in practice still be controlled though the order of emphletter/begemphword/endemphword/begemph/endemph/begemphphrase/endemphphrase/lenemphphrase rules. So if the author of a table really wants the bits to stay the same, he can.

However I wouldn't guarantee it for all tables. The bit order has never been part of the contract of a table (except for bold, italic and underline). If some systems depend on a specific order, they are not using the API correctly.