Refactor function to align with real function prototype

Align function documentation with that used in corresponding Holberton blog article

Use more explicit 'length' as variable instead of 'len'

Align strlen prototype with updates

Use size_t return type and receive string as const

Align implementation of memset with standard library prototype

Update function documentation to match that used in Holberton blog article

Update function documentation and set src parameter as const

Merge branch 'master' of https://github.com/bdbaraban/holbertonschool-low_level_programming

Make src parameter a constant

Make documentation more explicit

Always return byte difference and improve specifity of documentation

Point submodules to latest commits

Document Tests section

Upload folder with test file