feat: add a Boolean "path exists" function

[DavidVujic]

Description

Fixes issue #254

Motivation and Context

Avoiding a breaking change in the existing exists function, by adding a pathExists that will return a boolean value.

true if the path exists, false if not.

How Has This Been Tested?

npm test ok.
Added code to the examples, that runs the new functions.
CircleCI builds passed.

Types of changes

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

Checklist:

• I have read the code of conduct.
• I have read the contributing guide.
• I have updated the documentation accordingly (if applicable).