Support masking fields with terminals

json-mask is now able to mask fields with terminals by escaping them.

For example, {"a/b": 1} can be masked by a\\/b and {"*": 3} can be masked by \\*.
The general pattern is: escape the the masking language features by using: \\.

As this change alters the masking language, this is a breaking change necessitating the major version increase.
Along with the changes, the minimum Node engine has also been increased to the current Maintenance LTS v14.

Fixes issue #164

Thank you:

• @mochja for contributing the terminal escaping in PR #165
• @willfarrell for contributing the filtering of non-essential files from the NPM package in #125
• @YamiOdymel for correcting the language definition in the docs and comments #161