Release - 4.2.0

Summary
========
This release adds many new functions and fixes, and continues to be backwards compatible with stdlib 3.x

Features
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- New `base64()` function
- New `deep_merge()` function
- New `delete_undef_values()` function
- New `delete_values()` function
- New `difference()` function
- New `intersection()` function
- New `is_bool()` function
- New `pick_default()` function
- New `union()` function
- New `validate_ipv4_address` function
- New `validate_ipv6_address` function
- Update `ensure_packages()` to take an option hash as a second parameter.
- Update `range()` to take an optional third argument for range step
- Update `validate_slength()` to take an optional third argument for minimum length
- Update `file_line` resource to take `after` and `multiple` attributes

Bugfixes
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- Correct `is_string`, `is_domain_name`, `is_array`, `is_float`, and `is_function_available` for parsing odd types such as bools and hashes.
- Allow facts.d facts to contain `=` in the value
- Fix `root_home` fact on darwin systems
- Fix `concat()` to work with a second non-array argument
- Fix `floor()` to work with integer strings
- Fix `is_integer()` to return true if passed integer strings
- Fix `is_numeric()` to return true if passed integer strings
- Fix `merge()` to work with empty strings
- Fix `pick()` to raise the correct error type
- Fix `uriescape()` to use the default URI.escape list
- Add/update unit & acceptance tests.