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

lib/mdbx/database.rb

@@ -9,7 +9,6 @@ require 'mdbx' unless defined?( MDBX )
 #
 class MDBX::Database
 
-
 	### Open an existing (or create a new) mdbx database at filesystem
 	### +path+.  In block form, the database is automatically closed.
 	###
@@ -40,6 +39,7 @@ class MDBX::Database
 	# Only instantiate Database objects via #open.
 	private_class_method :new
 
+
 	# The options used to instantiate this database.
 	attr_reader :options
 
@@ -52,5 +52,17 @@ class MDBX::Database
 	# A Proc for automatically deserializing values.
 	attr_accessor :deserializer
 
+
+	# Allow for some common nomenclature.
+	alias_method :namespace, :collection
+	alias_method :reopen, :open
+
+
+	### Switch to the top-level collection.
+	###
+	def main
+		return self.collection( nil )
+	end
+
 end # class MDBX::Database