Improved formatting with par.
Fix intro Grammer.
Adds docs for the affinity feature.
Merges branch 'feature/add-affinity-docs' into develop
Adds warnings for conflicting mappings.

The `portkey_warn_on_mapping_conflict` option toggles these warnings. Default is
on, ie:- will show warnings. Warnings are only shown once.

Closes #2
Fixes conflict check conditional
Documents the 'warn_on_mapping_conflicts' option.
Merges branch 'feature/warn-on-mapping-conflict' into develop