Merge pull request #55 from 302dev/pr-55

Pull request replaces #54

Merge pull request #39 from tanakahisateru/fix-existing-zero-not-pres…

…erved

Preserve existing zero-like variables

Merge pull request #38 from josegonzalez/josegonzalez-patch-1

feat: lower the php version

feat: raise minimum php version

chore: reorder where functions are defined

Update example

Enhance documentation

Add RemapKeysFilter

Add the ability to pass in configuration to a given filter

This enables us to do interesting things, such as modifying a filter at runtime to whitelist keys from modification etc.

Merge pull request #24 from josegonzalez/josegonzalez-patch-2

Add testing to 5.6 and 7.0