Customize the file extensions associated to the languages

[echebbi]

Originally ask by @XLPmc in #48.

When developping in C++ it can happen that developers use the .h extension to define C++ headers. As a consequence, since the language is determined by the extension of the file, Discord always shows Programming in C while the actual programming language is C++.

It would be convenient to add an option to project Properties page allowing the developer to specify that the language used in this project is C++ even if the files have the .h extension.

[echebbi]

I don't have time to implement this at the moment.

Feel free to submit a PR if you want to contribute to the project.

[echebbi]

On second thought, I really don't want to implement something as specific as "provide X workaround for Y language". However, I can provide a way to customize the file extensions associated to each language, e.g. a table as follows:

Programming language	File extensions	Special files
Java	.java
C++	.cpp, .h
Docker		Dockerfile

I updated the name of the issue accordingly. Hopefully I'll find the time to implement it soon.