* core/rawdb, cmd, ethdb, eth: implement freezer tail deletion
* core/rawdb: address comments from martin and sina
* core/rawdb: fixes cornercase in tail deletion
* core/rawdb: separate metadata into a standalone file
* core/rawdb: remove unused code
* core/rawdb: add random test
* core/rawdb: polish code
* core/rawdb: fsync meta file before manipulating the index
* core/rawdb: fix typo
* core/rawdb: address comments
