Update syntax.yml (#119)

* Update syntax.yml

Adding offset_mode opcode and its page

* Create offset_mode.md

Adding page.

_data/sfz/syntax.yml

@@ -309,6 +309,16 @@ categories:
         max: 4294967296
         unit: "sample units"
 
+    - name: "offset_mode"
+      short_description: "Defines whether offset is measured in samples or percentage of sample length."
+      version: "ARIA"
+      value:
+        type_name: "string"
+        default: "samples"
+        options:
+        - name: "samples"
+        - name: "percent"
+
     - name: "sample"
       short_description: "Defines which sample file the region will play."
       version: "SFZ v1"

opcodes/offset_mode.md

@@ -0,0 +1,14 @@
+---
+layout: "sfz/opcode"
+opcode_name: "offset_mode"
+---
+An ARIA extension that can be used to set [offset] to a percentage of the
+total sample length, instead of being measured in sample units. It
+applies to both fixed offset and offset modulated by MIDI CC.
+
+## Examples
+
+```
+offset_mode=percent
+offset_oncc25=50
+```