API CHANGE: Remove bufferSizeInFrames and bufferSizeInMilliseconds.

These used to represent the size of the entire buffer, with the latency
defined by the the size of this buffer, divided by the period count.
This ended up being confusing because people assumed the buffer size by
itself was enough to define the latency. With this commit, these config
variables have been replaced with ones that take the size of a period
rather than the size of the entire buffer. These are called
periodSizeInFrames and periodSizeInMilliseconds. With this change, the
latency is determined by these settings alone, without needing to take
the period count into account. This should make things much easier to
understand.

This commit removes MA_BASE_BUFFER_SIZE_IN_MILLISECONDS_LOW_LATENCY and
MA_BASE_BUFFER_SIZE_IN_MILLISECONDS_CONSERVATIVE.

This commit removes ma_get_default_buffer_size_in_milliseconds() and
ma_get_default_buffer_size_in_frames().