Expose parse_line() globally.

Add new function readline_into_buffer() that allows the
output of readline to be put into a pointer to char buffer.

This refactoring allows other functions besides the
main command loop to also use the same input mechanism.

Signed-off-by: James Yang <James.Yang@freescale.com>
Acked-by: Jon Loeliger <jdl@freescale.com>