Linter_Bears_Advanced.rst: Update tutorial
Linter_Bears_Advanced.rst: Update tutorial

Add details about ``process_output_unified_diff``,
``process_output_corrected`` and ``process_output_regex``.

Closes https://github.com/coala/coala/issues/4120

coala/coala,coala-analyzer/coala,coala/coala,SanketDG/coala,SanketDG/coala,jayvdb/coala,coala/coala,coala-analyzer/coala,coala-analyzer/coala,SanketDG/coala,jayvdb/coala,jayvdb/coala