Add link in query docs to code showing all available query functions

[mieubrisse]

The examples don't show many of the functions available. Added a link in the docs to the code where the functions are defined.

---

[!IMPORTANT] Add link in querying-data.rst to source code for available query functions.

• Documentation:
  • Adds a link in querying-data.rst to the source code for all available query functions for complex queries.

^{This description was created by for 7d7abaa018b95ac7c5938b4f3a708834802c0f8a. You can customize this summary. It will automatically update as commits are pushed.}