zenity dialog implementation

[mgerhardy]

again no premake integration - but i've read in the readme that you would like to have something like this...

[mgerhardy]

could be extended to also support kdialog - but I don't have a kde env to test with.

[mgerhardy]

ups - forgot to implement --file-filter support - will leave that for someone else ;)

[onqtam]

will this get merged?

[mgerhardy]

premake and --file-filter support is still missing. Feel free ... ;)

[mlabbe]

Indeed, while a Zenity implementation is desirable, it must be fully featured and easy to build. This lib has hundreds of users and I want to make sure they don't fall into the trap of opting for a backend that doesn't meet the features described in the readme.

This PR needs work before it can be merged. In addition to premake and --file-filter support, please see:
https://github.com/mlabbe/nativefiledialog/blob/master/docs/submitting_pull_requests.md

[mlabbe]

An alternative Zenity impl was merged to devel today which builds with Premake. Took a look to see if it suits your needs!