Create a memory bitmap and implement malloc

[xbhatnag]

Currently very few pages are mapped in the MMU to get the kernel working.
But the OS has no idea about the overall usage of physical memory.
There needs to be a memory bitmap. Get total number of pages in physical memory.
1 bit for each - used or not?

This leads the way to malloc working correctly. Kernel asks for memory? Ok. Find a free page. Mark it used. Zero out the bits. Return an address.

We aren't always pulling out new pages though. This gets complicated when we need to find free space within a used page. How does that work?