Add option to output result in C include file style (#242)

[wpcwzy]

This pull request introduces a new feature that adds an option to output the result in C include file style, similar to the -i or --include option of the xxd command. This functionality allows users to generate hex dumps in a format that can be easily embedded as arrays in various programming languages.

When hexyl accepts input from stdin, users can expect the following output format:

$ echo -n "Hello, world!" | hexyl -i
  0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x2c, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64,
  0x21

When hexyl accepts a filename as an argument and reads from the file, users can expect the following output format:

$ hexyl -i hello.txt
unsigned char hello_txt[] = {
  0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x2c, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64,
  0x21
};
unsigned int hello_txt_len = 13;

The above behavior is consistent with the behavior of xxd -i.

I also added the functionality to accept input from a slice and output the bytes in C include file style, as I noticed that there is a corresponding use case in examples/simple.rs. When hexyl accepts input from a slice, its behavior is consistent with accepting input from stdin.

This is my first time contributing a new feature to an open-source project, so if there are any areas where I may have fallen short or could improve, I would really appreciate your feedback. Thank you!