Multiple changes.

- Raise an error if invalid options are passed to the constructor.
- Bugfix: Ensure drop() only removes the specified collection.
- Fix initializer double memory allocation.
- Fix key/data object allocation: make garbage collection safe.
- Move common macros to the global header file.

FossilOrigin-Name: 98d3016bd25921dead39d9c5474712766b56519d575bc8cd960932b3fbc16b69

.pryrc

@@ -11,5 +11,6 @@ rescue Exception => e
 		e.backtrace.join( "\n\t" )
 end
 
-db = MDBX::Database.open( 'tmp/testdb', max_collections: 100 )
+db = MDBX::Database.open( 'tmp/testdb', max_collections: 50 )
+#db = MDBX::Database.open( 'tmp/testdb', duplicate_keys: true )