lowering recall threshold

[scicco]

Description

This is my first attempt to try to contribute a bit to this awesome project😹
This commit will lower the recall threshold. It also separates the config introducing the RecallSettings class as suggested in TODO

I've set the following constant values:

    DEFAULT_K = 3
    DEFAULT_TRESHOLD = 0.5

please let me know if those values are appropriate.

Related to issue (#909)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

[valentimarco]

Thx for the contribution! For me is ok but i would prefer to have a central module to store all classes like this one. What do you think @pieroit ?