Add Floating Islands and material-driven Age features (#45)

Keep repeated feature and material pages in authored writing, vary their resolved materials, and expose Link Panel modifier variants in creative and JEI. Remove Descriptive Book writing notes and refine Void biome selection.

src/main/resources/assets/rivencraft/lang/en_us.json

@@ -95,9 +95,6 @@
   "screen.rivencraft.age.pages": "Pages",
   "screen.rivencraft.age.details": "Details",
   "screen.rivencraft.age.pages_count": "Writing %s/%s",
-  "screen.rivencraft.age.writing_notes": "Writing notes",
-  "screen.rivencraft.age.writing_general": "Book",
-  "screen.rivencraft.age.writing_page": "Page %s",
   "screen.rivencraft.age.trait.biomes": "Biomes: %s",
   "screen.rivencraft.age.trait.lighting": "Lighting: %s",
   "screen.rivencraft.age.trait.weather": "Weather: %s",
@@ -231,7 +228,7 @@
   "symbol.rivencraft.phase.setting.description": "Set the celestial phase to setting.",
   "symbol.rivencraft.feature.caves": "Caves",
   "symbol.rivencraft.feature.caves.description": "Add extra caves to the chosen noise terrain.",
-  "symbol.rivencraft.block.generated.description": "Material modifier; place immediately before a compatible feature page.",
+  "symbol.rivencraft.block.generated.description": "Place before a compatible feature page, or let the Age choose a compatible feature.",
   "symbol.rivencraft.feature.flowers": "Flowers",
   "symbol.rivencraft.feature.flowers.description": "Add vanilla flower patches to surface terrain.",
   "symbol.rivencraft.feature.trees": "Trees",
@@ -246,6 +243,8 @@
   "symbol.rivencraft.feature.deep_lakes.description": "Add underground lakes using a random fluid, or specify one with a fluid page.",
   "symbol.rivencraft.feature.ravines": "Ravines",
   "symbol.rivencraft.feature.ravines.description": "Add vanilla canyon carving to noise terrain.",
+  "symbol.rivencraft.feature.floating_islands": "Floating Islands",
+  "symbol.rivencraft.feature.floating_islands.description": "Add high floating islands above the chosen surface terrain.",
   "symbol.rivencraft.feature.lava_lakes": "Small Lakes",
   "symbol.rivencraft.feature.lava_lakes.description": "Add small surface lakes using a random fluid, or specify one with a fluid page.",
   "generator.rivencraft.standard": "Standard",

src/main/resources/data/rivencraft/rivencraft/symbols/feature/floating_islands.json

@@ -0,0 +1,8 @@
+{
+  "schema_version": 2,
+  "name": "symbol.rivencraft.feature.floating_islands",
+  "description": "symbol.rivencraft.feature.floating_islands.description",
+  "category": "rivencraft:feature",
+  "semantics": { "role": "feature", "value": "rivencraft:floating_islands" },
+  "poem": "Terrain Elevation Island Sky"
+}