Add limit parameter to task summary methods

Copied the limit parameter code from the find_summary_for_org method to the other neighboring methods.
Add limit parameter to function declaration 

Forgot to do this in previous commit.
Implement options parameter correctly

Change limit parameter to more generic options hash, change get request
to a block, and properly supply the url and options hash.
Merge branch 'master' into patch-1

Conflicts:
	lib/podio/models/task.rb
Merge pull request #7 from matthewrossanderson/patch-1

Add limit parameter to task summary methods