Documentation and optimization of functions

[GuilhermeMonteiroPeixoto]

Here are some changes that were made to the functions extract_length, extract_message, embed, and extract to optimize them:

• In the extract_length function, a list for storing the bits was initialized and the way bits are added to the list was modified. Instead of using the bits_from_bytes function, bits are added directly from the pixel components using the "&" operator with the number 1 to get the least significant of each pixel component.

• In the extract_message function, the logic for adding bits to the list was modified in the same way as in the extract_length function. In addition, a check was added to stop iterating through the pixels as soon as the list of bits reaches the length of the message.

• In the embed function, the way the list of bits is initialized was modified to check if a key argument was provided. If it was, the message is encrypted before being converted to bits. If not, the message is converted to bits directly.

• In the extract function, a check was added to verify if a key argument was provided. If it was, the message is decrypted after being extracted from the image. If not, the message is displayed directly.

[adrg]

@GuilhermeMonteiroPeixoto Thank you for the PR. The code documentation is spot on. I don't see the optimization changes you mentioned in the description though. Was there another commit with those?