Make the matroska_info output compatible with mkvinfo from mkvtoolnix

[lu-zero]

mkvtoolnix mkvinfo and matroska_info have more or less the same purpose.

• report position and size for each element
• report the Seek entries

|+ Seek head at 0x3b size 71
| + Seek entry at 0x47 size 14
|  + Seek ID: 0x15 0x49 0xa9 0x66 (KaxInfo) at 0x4a size 7
|  + Seek position: 229 at 0x51 size 4
| + Seek entry at 0x55 size 15
|  + Seek ID: 0x16 0x54 0xae 0x6b (KaxTracks) at 0x58 size 7
|  + Seek position: 316 at 0x5f size 5

• Fix the capitalization