Support for selecting quickjs-ng as quickjs source code.

[ahaoboy]

Currently, the git submodule is used to download the qjs source code. It would be beneficial to have the ability to use a feature to select quickjs-ng as the source code for compilation. Alternatively, supporting the use of an environment variable to set a git link for dynamic source code download in the build.rs, it would be useful for compiling a modified version of qjs, as long as they have the same interfaces.

[Sytten]

I feel as the projects want to merge in the near future it would not be time well spent but I could be wrong.

[DelSkayn]

The readme of quickjs-ng seems to support the fact that the want to merge. Therefore I am going to close this issue as wontfix. Upstream quickjs will most likely eventually support the features of quickjs-ng so selecting between forks won't be necessary