Support pathlib.Path() objects

[singingwolfboy]

Fixes #345. This change allows Rollbar to convert pathlib.Path objects to regular strings for serialization purposes. This also prevents Rollbar from crashing in the default Django configuration, where settings.BASE_DIR is a PosixPath object.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Maintenance
• New release

Checklists

Development

• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer

[danielmorell]

@singingwolfboy Thank you for putting this together! This looks great!