Move spec/registry.md -> spec/registry/default.md

Author: eemeli

spec/README.md

@@ -16,7 +16,7 @@
    1. [Data Model Errors](errors.md#data-model-errors)
    1. [Resolution Errors](errors.md#resolution-errors)
    1. [Message Function Errors](errors.md#message-function-errors)
-1. [Default Function Registry](registry.md)
+1. [Default Function Registry](registry/default.md)
 1. [Formatting](formatting.md)
 1. [Interchange data model](data-model/README.md)
 

spec/registry.md renamed to spec/registry/default.md

@@ -548,7 +548,7 @@ whether an _operand_ is required,
 what form the values of an _operand_ can take,
 what _options_ and _option_ values are valid,
 and what outputs might result.
-See [function registry](./registry.md) for more information.
+See [function registry](/spec/registry/default.md) for more information.
 
 A _function_ starts with a prefix sigil `:` followed by an _identifier_.
 The _identifier_ MAY be followed by one or more _options_.