ESPTerm "Damselfly" pre-release

This is a pre-release of the upcoming release 2.4.0 codenamed "Damselfly".

The key addition this release brings is an API for remote access to some GPIO pins. I suggested this feature as a nice-to-have improvement in September 2017, and thanks to @schneemaier's periodic reminding (for a good half a year), I finally implemented it today.

This huge delay was in part caused by me finishing my studies and working on the thesis project [1], and then getting distracted by another side project [2]. Now both are somewhat finished, and I'm out of the university,
but my free time has only diminished thanks to full-time employment.

[1]: https://gex.ondrovo.com/ (I intend to work on this again in the near future)
[2]: https://datatable.directory/ (beta, work in progress, but functional)

Anyway, enjoy the release and report any bugs so I can make a sharp 2.4.0 soon.

Known issues: the Hungarian translation needs an update.