terminal-emulator.sh tmux implementation and base unit tests

- terminal-emulator.sh is a script that takes a log file as input and
uses a detached tmux session to cat the log file to the terminal,
and then save the contents of the pane history to an output log file.
The output log file now emulates the contents displayed on a terminal
Five  basic tests are included in test-terminal-emulator.sh
which run through ^H input during prompts, as well as VT100 escape
sequences from parts of various log files, as well as testing the
emulation of an on-screen GRUB MENU.
- Added test-terminal-emulator which implements base unit tests
to validate expected output versus generated output of special
escape characters such as backspace and menu characters.
- Added dependency information about terminal-emulator and
  a description/usage paragraph.

Signed-off-by: Abhi Singh <Abhi.Singh@arm.com>