Suggestion: add functions for performance stats

suggested replacements for old profile() function

elapsed() = time elapsed since f3 loaded; 
default to return with label showing micro | milli | seconds
note range boundary, above 0.09 uses seconds, easier to read .33 seconds than 330 milliseconds

memory() = memory used by php script; 
default to peak memory, default to return with label showing KB | MB

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add mapper method castall()
to accommodate the need to cast multiple mappers returned from a find() operation.
https://groups.google.com/d/topic/f3-framework/zz8fy69cd7k/discussion

even though a pure exec(select ) etc is slightly faster, when you want to use mappers for ease of use and want to work with multi-dim assoc arrays, this additional method is easier than writing an array_map call in your code

// get find() results into multi row mapper
$mapper_multi_row = $mapper_object->find($criteria,$order_by);
// then pass that array to castall() method
$mapper_multi_row_casted_to_multidim_array = $mapper_object->castall($mapper_multi_row);