Make 'rake build' and 'rake install' work again

This needs require 'bundler/gem_tasks' in Rakefile
RUBY-596 Adding in base aggregation class
RUBY-596 Rename #immutable #new
RUBY-596 Iterate results of an aggregation with no cursor
RUBY-596 Add #aggregate to collection view
RUBY-596 Always return a cursor on aggregate
RUBY-596 First implementation general result to pass to cursor
User generic result in command
RUBY-596 Create and remove user ops use generic result
RUBY-596 Delete operation uses generic result
RUBY-596 Ensure and drop index use generic result
RUBY-596 Insert uses generic result
RUBY-596 Update uses generic result
RUBY-596 Alias n to written_count
RUBY-596 Fixing rdoc
RUBY-596 Query and GetMore return result objects
Pass result objects to the cursor
RUBY-596 Aggregation results work sans cursor
RUBY-596 Aggregation results work with cursor and all batch sizes
RUBY-596 Aggregation results work on 2.4