Rename mem_map to mMap, remove some in_memory variables being passed around, added MemoryMapped member to volume struct

weed/storage/memory_map/memory_map.go

@@ -0,0 +1,23 @@
+// +build !windows
+
+package memory_map
+
+import "os"
+
+type MemoryBuffer struct {
+	aligned_length uint64
+	length         uint64
+	aligned_ptr    uintptr
+	ptr            uintptr
+	Buffer         []byte
+}
+
+type MemoryMap struct {
+	File                   *os.File
+	file_memory_map_handle uintptr
+	write_map_views        []MemoryBuffer
+	max_length             uint64
+	End_Of_File            int64
+}
+
+var FileMemoryMap = make(map[string]MemoryMap)