Running glad twice is not reproducible
Running the following commands:
```
glad --out-path glad1 --generator c --profile core --omit-khrplatform --spec gl --api gl=3.3
glad --out-path glad2 --generator c --profile core --omit-khrplatform --spec gl --api gl=3.3
```
will generate 2 glad opengl 3.3 core loaders in the directories `glad1` and `glad2`.

The two directory trees are different however:
- they contain a different timestamp; and
- the order in which some global variables are defined in `glad.c` is different.

I would suggest to:
- add no timestamp by default or add a `--reproducible`/`--notimestamp` command line option; and
- explicitly order all variables.

Using `pip 0.1.26` from pypi