Add ISO 259

[charlesLoder]

Add a schema for ISO 259

[BillMeyerRSA]

Question:
What does null do?
I see in the schema the *_DAGESH for sbl have null in the json schema.
"BET": "b",
"BET_DAGESH": null,

Would there be a difference if it was:
"BET": "b",
"BET_DAGESH": "b",

[charlesLoder]

Nope, no difference at all