add fun "emysql:as_maps/1"

Hi!
I added the fun "emysql:as_maps/1".
And the test result:
21	basics_SUITE	conversion	maps_empty_test	< >	0.000s	Ok	
22	basics_SUITE	conversion	maps_single_test	< >	0.000s	Ok	
23	basics_SUITE	conversion	maps_multi_test	< >	0.000s	Ok