Implement "give me memory" and "reclaim this memory" system call to allocate kernel heap memory to processes

[gustrain]

Requires #6 to test

[gustrain]

Some potentially useful resources:

• https://www.valvers.com/open-software/raspberry-pi/bare-metal-programming-in-c-part-4/#the-arm-timer-peripheral
• https://developer.arm.com/documentation/dui0662/b/The-Cortex-M0--Instruction-Set/Miscellaneous-instructions/SVC