This change adds the ability to perform reads from freezer without size limitation. This can be useful in cases where callers are certain that out-of-memory will not happen (e.g. reading only a few elements).
The previous API was designed to behave both optimally and secure while servicing a request from a peer, whereas this change should _not_ be used when an untrusted peer can influence the query size.
* 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
