Second .projlint.yml file support

[Cihat Gündüz]

Currently when using .projlint.yml and using the rule file_content_template and comparing the file with a remote template, it's sometimes a little inflexible to not be able to add project-specific additional rules that only apply in this project. There could be either support for specifying multiple .yml files to solve this problem or a default second yml file which can be used to define project-specific rules. The default second file could be named .projlint-local.yml or .projlint-private.yml.