Multiple changes.

- Provide a method to reopen the database environment if closed.
 - Add #keys, which returns an array of keys for the current collection.
 - Finish collection/namespace implementation.
 - Add various aliases (collection->namespace, etc)
 - Add #clear, which destroys data for a the current collection.
   If called in the main db, destroys all.  Don't close the environment
   after a #clear, just the dbi handle.
 - Various bugfixes.

FossilOrigin-Name: 8b00d59e8c5269266f3c6c0d10056a1c0fe1bb583ffbe099a6ed0dac3baf3a66

spec/lib/helper.rb

@@ -14,7 +14,7 @@ require 'mdbx'
 
 
 module MDBX::Testing
-	TEST_DATABASE = Pathname( __FILE__ ).parent.parent + 'data' + 'testdb'
+	TEST_DATABASE = Pathname( __FILE__ ).parent.parent.parent + 'tmp' + 'testdb'
 end