* clarify "cancelled periodic snapshot" message
* more rigorous checks for snapshot validity
* verify ancient blocks on import
* limit number of fed blocks
* make it possible to feed snapshot service canonical hashes
* fix failing test build
* swap ethash DAG only when more recent
Implementations of get_cache_size and get_data_size in Rust (issue #161)
Removed sizes module, containing replaced data tables
Fixed whitespace issues after code review