API for 12 bits temp values

- New functions getTemp, rawToCelsius and rawToFahrenheit to support raw
12 bit integer temp values (1/16 of degree Celsius).
- Improved performance of temp conversion with integers arithmetic - http://myarduinotoy.blogspot.co.uk/2013/02/12bit-result-from-ds18s20.html
- No more issues with DS18S20
- Can also work with DS1825
- Fix typos in comments

I think something is wrong with my commit since it shows the entire file was updated.