Added Buffer.initCapcity() to buffer to allow preallocation of a block of memory to reduce future allocations. Uses the added ArrayList.initCapacity() function to achieve this.

Added Buffer.capacity() to track current usable allocation size, not counting null byte, and returning 0 if empty or created with Buffer.initNull()

Added a test for initCapacity() that shows that no further allocation is performed for an append of size smaller than or equal to capacity when initCapacity is used.

Added a test for initSize(), since it did not exist already.

Also added a comment to better explain the difference between initSize() and initCapacity()

note: forgot in the first commit but thanks to mikdusan for helping me brainstorm, through the process, and for drawing up a draft diff which I tweaked.