Multiple changes.

- Alter the behavior of #clear, so it doesn't destroy collection
   environments, but just empties them.
 - Add #drop, which explictly -does- destroy a collection environment.
 - Run all cursor methods through rb_protect, to ensure proper
   cursor cleanup in the event of an exception mid iteration.
 - Fix the block form of collections to support multiple scopes.
 - Switching to a collection now automatically creates its environment.
 - Add include? and has_key?, for presence checks without allocating
   value memory or requiring deserialization.

FossilOrigin-Name: e1ed7bf613981607bb3b57ce7dd3e58b94ea3046e140b6dc37440da8d2909f94

lib/mdbx.rb

@@ -10,7 +10,7 @@ require 'mdbx_ext'
 module MDBX
 
 	# The version of this gem.
-	VERSION = '0.2.1'
+	VERSION = '0.3.0'
 
 end # module MDBX