Add MCP4151 library

[nwb99]

Add MCP4151 digital pot library

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/nwb99/MCP4151:

Linting library in MCP4151
WARNING: library.properties version value 1.0 is not compliant with the semver specification.
         See: https://semver.org/                                                            
         (Rule LP021)                                                                        
WARNING: No example sketches found. Please provide examples.                                      
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#library-examples
         (Rule LD004)                                                                             

Linter results for project: 0 ERRORS, 2 WARNINGS

-------------------

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/nwb99/MCP4151/