c: Implement the CLI tool

The CLI tool should have feature parity with the Python equivalent.

Both implementations generate the same hashes so the algorithm seems to
be sound.

c/cli/meson.build

@@ -1,2 +1,2 @@
-executable('passgeny', 'src/passgeny.c', dependencies: phogen_dep)
+executable('passgeny', 'src/main.c', dependencies: [passgeny_dep])