Changed a function name and a variable name for clarity and consistency.
Changed a function name and a variable name for clarity and consistency.

`prof_end_trial` was renamed to `prof_stop_trial` to better juxtapose
`prof_start_trial`.

The `p_data` struct's `num_trials` member was renamed to `max_trials` to better
reflect its use as a memory limit and not an experimental value.

ChrisTM/simple-prof