Library for the DS1620 Digital Thermometer

This pull request has been accepted and merged in by Ryan Bancroft

Optimization and Warning resolution

There are following changes: 1. Warnings resolved: implicit type conversion float to double and back to float 2. Optimization: wait for write operation completion changed from wait(float) to wait_ms(int)

Optimization of original DS1620 library - calls to wait(float) changed to wait_us(int) + resolving several warnings. DS1620, measurement, Temperature