Drop Emacs 24 Support

[zonuexe]

We have plans to drop support for Emacs 24 and 25.1 with the first release in January 2020.

Our support policy:

Support Emacs Version · Issue #464 · emacs-php/php-mode

We can release support for older Emacs from the stable branch if needed, but be aware that it is not provided by MELPA.

Before (current)

Version	Support
27(dev)	Supported
26.3	Recommended
26.2	Supported
26.1	Supported
25.3	Supported
25.2	Supported
25.1	Compatible, but it is not tested.
24.5	Supported, until 2020.
24.4	Compatible, but it is not tested.
24.3	Supported, until 2020.
≦ 24.2	No longer supported

After

Version	Support
27(dev)	Supported
26.3	Recommended
26.2	Supported
26.1	Supported
25.3	Supported
25.2	Supported
≦ 25.1	No longer supported

Discussion about dropping Emacs 23

• #214 Adjust Minimum Emacs Version?
• #247 Drop Emacs 23 Support