Rewrite of the Lua DS18B20 module

[vsky279]

Implements suggestions discussed in #1883 and flaws pointed out in #1820 with @TerryE.

Make sure all boxes are checked (add x inside the brackets) when you submit your contribution, remove this sentence before doing so.

• This PR is for the dev branch rather than for master.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at README.md.

Features:

• the module is fully asynchronous (no use of tmr.delay)
• supports powered and parasitic-powered devices and its combinations on the same bus
• both float and integer versions of Lua are supported
• optional storing and retrieval of address to flash

Feel free to comment and suggest further improvements.