Kick-off work on Proxy-Wasm ABI vNEXT.

[PiotrSikora]

No description provided.

[PiotrSikora]

Note: This only copies v0.2.1 spec (with minor changes to the version number), so that we can apply changes individually via PRs instead of having one big update that's impossible to review.

--- abi-versions/v0.2.1/README.md       2024-08-09 17:44:06.036661934 -0400
+++ abi-versions/vNEXT/README.md        2024-12-19 13:46:48.945684739 -0500
@@ -1,8 +1,8 @@
-# Proxy-Wasm ABI v0.2.1 specification
+# Proxy-Wasm ABI vNEXT specification
 
 ---
 
-Status: **FINAL** (corrections and/or clarifications are welcomed)
+Status: **WORK-IN-PROGRESS**
 
 ---
 
@@ -53,7 +53,7 @@
 
 ### Callbacks exposed by the Wasm module
 
-#### `proxy_abi_version_0_2_1`
+#### `proxy_abi_version_0_x_x`
 
 * params:
   - none
@@ -61,7 +61,7 @@
   - none
 
 Function marker used during linking to advertise Wasm module's support
-for Proxy-Wasm ABI v0.2.1.
+for Proxy-Wasm ABI vNEXT.
 
 This function is never called.
 
@@ -2085,7 +2085,7 @@
 [memory management]: #Memory-management
 [serialized]: #Serialization
 
-[`proxy_abi_version_0_2_1`]: #proxy_abi_version_0_2_1
+[`proxy_abi_version_0_x_x`]: #proxy_abi_version_0_x_x
 [`_initialize`]: #_initialize
 [`main`]: #main
 [`_start`]: #_start