Release 0.15.0

Chore:

• chore: increment version
• chore(deps-dev): updated dependencies
• chore(deps-dev): updated eslint dependency

Fix:

• fix(attributes): return null when null given and casting to Date
  • Closes #304
• fix(model-collection): improved duplicate methods typings

Documentation:

• docs: wording changes
• docs(collection): add missing static badges
• docs: added cookbook entry
• docs(collection): moved partition documentation to alphabetical order

Feature:

• feat(collection): add partition method
• feat(ancestry-collection): added AncestryCollection

Performance

• perf(model-collection): simplified hasDuplicates method

Refactor

• refactor(query-builder): moved operator values to method
  • This will mean less clutter when logging out a model on the console

Testing:

• test(model-collection): added tests for hasDuplicates
  • This ensures argument type validity.