* Removed pcall(require, "plugins.language_c") since it doesn't works
as it seems to have been intended.
* Removed duplicate keywords
* Added support for magic and uppercase constants.
* Basically merged most changes from the lite-xl-plugins repo.
Brought form the 1.16.12 release.
It provides support for C++ using multi-part syntax patterns. Take
the priority over C language plugins for header files.