Add 'n' depth stack for src attribute

[nathHy]

This PR adds the ability to change the src depth via an integer value instead of a boolean
Related to #72

This allows users to wrap their logger in functions and still maintain the correct src path/filename/function call when viewing logs.

• Updated readme
• Updated tests
• Fixes small typo in contributing.md

Let me know if theres anything I missed

Also I couldn't get the make check to function correctly. It kept complaining about /bin/sh not having [[
but it still passed the linter

[nathHy]

@trentm Any updates on this one?

[EricByers]

This would be helpful, since we ran into the same issue with src: true and wrapped logger methods.

[Sonivaibhav26]

@trentm Any updates on this one?