c: use valid C and puts instead of printf

[deltabeard]

Reduces compiled binary from 137kB to 115kB with cl /O1 hello.c. The binary is reduced from 32kB to 14kB when compiled with w64devkit using gcc -Os -s hello.c.

Returning a value in main() is required in C.

[MichalStrehovsky]

The k&r c programming language book starts with printf for hello world. It is the canonical thing. Please look at the rules in Readme.md.

[deltabeard]

Thanks. The rules mention that it is "ideal" to be in some tutorial.