Made unit configurable and set the default to milliseconds

When you're profiling you are usually looking at slow stuff so having numbers displaying per 0.1 microseconds is a tad unreadable usually 😄

So... with this change the default unit is set to milliseconds which makes everything a lot easier to read. The precision can be configured through the UNIT constant but if that's desired it might be better to move the constant elsewhere:

from line_profiler_pycharm import _profile


_profile.UNIT = 1e-6