Allow for a key:value representation of neumes and syllables

[anaskaejdar]

Kassia currently separates neumes and syllables, so that the neumes can be a whole body of text and the syllables can also be a whole body of text, rather than either being broken into pieces and paired together with their corresponding symbols from the other camp.

@ilizol requested that kassia use a key:value pair, similar to the syntax of https://github.com/muraiki/byzscribe