Fixed some syntax color issues.

Added .tex as a supported format.  In the process, redid the syntax
coloring slightly, to better support general regex's inside of quotes
and comments.

To do: remove explicit "\e" codes from this change and replace with
general "escape" character specification from Terminal class.

	modified:   editor.rb
bugfix: handle large negative line number.

	modified:   editor.rb
updated history file for 0.2.1 bugfix release

	modified:   HISTORY.md