implement basic kernel printing functionality

[ta5een]

Depends on #25

Implement basic functionality of the following functions to be used in the kernel for logging and debugging purposes:

• printf, snprintf, sprintf, vprintf
• putc, putchar
• puts

Stream-oriented versions (such as fprintf) are out of scope until file I/O capabilities are implemented. As a result, the concepts of stdout and stderr will not be applicable and will not be implemented for now.

For now, the functions listed above should output all strings to the serial port and the VGA text buffer.

Future considerations:

• Implementing logging levels (debug, info, error, etc.) for filtering log messages. See implement simple kernel logging interface #22.
• Ensuring thread safety in concurrent environments.
• Introducing buffering to optimise output performance.