Read Distro name from /etc/os-release

[pludi]

• Reads the Distro name from /etc/os-release
• Code paths only compiled on Linux
• As requested in feat: read os-release for distribution name #240 hidden behind new option
• Explanation in ARGS.md

Not tested on BSD, macOS, Windows since I don't have any of those systems available.

[angelbuggirl]

no

[angelbuggirl]

nevermind yes

[MrGlockenspiel]

Handful of issues:

• getline() isn't a standard function so it breaks Windows builds (or any other non-POSIX platform)
• You leak both pretty and fallback in get_release_info(), and the return value is also leaked and unreachable when you call strcat() directly on the function call like that
• The function copy_value() really has no reason to be exposed, it can be a static helper
• The header osrelease.h is unguarded
• FILE *osrelease is never closed

Other than those it looks good, I'll probably accept this and then commit the fixes since I've already written them, thank you