add region file format specification

doc/specs/binary_json_spec.md

@@ -49,9 +49,3 @@ int32     = 4byte
 int16     = 2byte
 byte      = %x00-FF
 ```
-
-## VoxelEngine format support
-
-Current implementation does not support types: bytes array, null, compressed document. 
-
-All unsupported types will be implemented in future.

doc/specs/region_file_v2_spec.md

@@ -0,0 +1,41 @@
+# Region File (version 2)
+
+File format BNF (RFC 5234):
+
+```bnf
+file    = header (*chunk) offsets   complete file
+header  = magic %x02 %x00           magic number, version and reserved
+                                    zero byte
+
+magic   = %x2E %x56 %x4F %x58       '.VOXREG\0'
+          %x52 %x45 %x47 %x00
+
+chunk   = int32 (*byte)             byte array with size prefix
+offsets = (1024*int32)              offsets table
+int32   = 4byte                     signed big-endian 32 bit integer
+byte    = %x00-FF                   8 bit unsigned integer
+```
+
+C struct visualization:
+
+```c
+typedef unsigned char byte;
+
+struct file {
+	// 10 bytes
+	struct {
+		char magic[8] = ".VOXREG";
+		byte version = 2;
+		byte reserved = 0;
+	} header;
+	
+	struct {
+		int32_t size; // byteorder: big-endian
+		byte* data;
+	} chunks[1024]; // file does not contain zero sizes for missing chunks
+	
+	int32_t offsets[1024]; // byteorder: big-endian
+};
+```
+
+Offsets table contains chunks positions in file. 0 means that chunk is not present in the file. Minimal valid offset is 10 (header size).