Move reference for function hashing into the 'function-space hashing' part of the docs (was erroneously placed under the 'LSHFunction API' section).

Author: kernelmethod

docs/src/function_hashing.md

@@ -131,5 +131,5 @@ julia> length(hashfn.sample_points)
 512
 ```
 
-## Footnotes
-
+## References
+- Shand, William and Becker, Stephen. *Locality-sensitive hashing in function spaces*. [arXiv:2002.03909](https://arxiv.org/abs/2002.03909).

docs/src/lshfunction_api.md

@@ -156,6 +156,3 @@ LSHFunctions.jl provides a few common utility functions that you can use across
          collision_probability(hashfn, sim; n_hashes=1)^5
   true
   ```
-
-## References
-- Shand, William and Becker, Stephen. *Locality-sensitive hashing in function spaces*. [arXiv:2002.03909](https://arxiv.org/abs/2002.03909).