Merge pull request #14 from Hugoberry/pbix2vpax

* Support for files with a signature `This backup was created using multithreaded XPrs9.`
* Expand VPAX serialisation for the old metadata.sqlite schema.
* RLS via `TablePermissions`

Author: Hugoberry

README.md

@@ -96,7 +96,7 @@ pbix2vpax(filename)
 - `UserHierarchies` - User-defined hierarchies
 - `Partitions` - Partition information including refresh times
 - `ColumnsSegments` - (Reserved for future use)
-- `TablePermissions` - (Reserved for future use)
+- `TablePermissions` - Row Level Security details
 - `CalculationItems` - (Reserved for future use)
 
 #### Basic Usage

data/rls.pbix

@@ -0,0 +1,67 @@
+meta:
+  id: abf_mt_xpress9
+  endian: le
+
+seq:
+  - id: signature
+    size: 102
+    type: str
+    encoding: UTF-16LE
+    doc: This backup was created using multithreaded Xprs9.
+  - id: multi_thread
+    type: thread_distribution
+  - id: chunks
+    type: chunk
+    repeat: eos
+    
+types:
+  thread_distribution:
+    seq:
+    - id: tail_block_count 
+      type: u8
+    - id: head_block_count 
+      type: u8
+    - id: head_thread_count 
+      type: u8
+    - id: tail_thread_count 
+      type: u8
+    - id: chunk_uncompressed_size
+      type: u8
+  chunk:
+    seq:
+    - id: uncompressed
+      type: u4
+    - id: compressed
+      type: u4
+    - id: node
+      type: node
+      size: compressed
+
+  node:
+    seq:
+    - id: header
+      type: header
+    - id: segments
+      size: _parent.compressed - 32
+      
+  header:
+   seq:
+    - id: xpress_magic
+      contents: [0x2a, 0xd7, 0x86, 0x4e]
+      doc: 0x4e86d72a [0x2a, 0xd7, 0x86, 0x4e]
+    - id: orig_size
+      type: u4
+    - id: encoded_size
+      type: u4  
+    - id: huffman_table_flags
+      type: u4
+    - id: zero
+      type: u4
+    - id: session_signature
+      type: u4
+    - id: block_index
+      type: u4
+    - id: crc32
+      type: u4
+   
+