Automatically create gitignore for build artifacts

[awvwgk]

Build systems like meson put a .gitignore in the build directory to avoid accidentally committing in the repository.

# This file is autogenerated by Meson. If you change or delete it, it won't be recreated.
*

Fpm could also put a .gitignore in the build directory with just * to avoid committing any build artifacts.

[urbanjost]

An fpm new subcommand makes a .gitignore with the line 'build/*' in it, but I do like your suggestion. I think the gitignore in the build/ directory makes perfect sense, as everything in there is generated by fpm. The only hesitation might be that if someone is using git(1) for more than just generating a standard fpm directory, they might actually WANT to push or pull the entire directory, perhaps to a mirror in their own organization, for example. Perhaps only making it when the build/ directory is created is OK, and not checking for it at each execution (which I think is what you were suggesting anyway) is OK, especially since not everyone initializes a package with new but just creates it manually or some other way; but I would like a line mentioning that somewhere in the user guide saying you need to delete it in that case. I think it is desirable such a high percentage of the time that it does not need a .command switch on fpm itself. Would we then get rid of the one generated in the top of the package curr i ently by new? I think I would, as it would be redundant and could just lead to confusion and it is neater if everything generated by fpm is in the build directory whenever possible. What does Meson do for hg or other packages? Would you just make a .hgignore as well, or only make a .gitignore if you saw a .git directory, and/or a .hgignore if you saw a .hg/ directory?

Currently, we just pre-suppose git(1) is being used, and even expect it if you want to use dependencies; but other package managers allow any or a list of other packages to be used. Will we always pre-suppose git(1) is being used?