Added support for Honeywell HMC5883L digital compass

[jschmidlapp]

No description provided.

[marcelstoer]

Can't comment on the C code but on a number of formalities. See https://github.com/nodemcu/nodemcu-firmware/blob/dev/CONTRIBUTING.md#writing-documentation:

• we appreciate descriptions for PRs
• modules in user_modules.h should be alphabetically sorted a-z
• module documentation should be added to mkdocs.yml
• modules in mkdocs.yml should be alphabetically sorted a-z
• functions in the module documentation should be alphabetically sorted a-z

[TerryE]

This check is redundant so drop it; the check integer calls do this anyway. Also use the arg check macro instead of an if predicate and an error call: less source lines and a better diagnostic for the app programmer.

[jmattsson]

👍 with similar comments as on #1252.