Add c-mode key binding for header guard

When in c mode (cc-mode), "C-c h" is added as a key binding to the
c-mode-map to insert a header guard like so.

	// my_file.h
	#ifndef __MY_FILE_H
	#define __MY_FILE_H

	#endif /* #ifndef __MY_FILE_H */

The function that does the insert is interactive, so it will prompt you
for the guard, offering the equivalent to the above for your file as the
default.
Add logic to pick first available font in Windows

XP doesn't have our preferred font, so we provide a list and pick the
first one that matches.
Add cmake-mode and markdown-mode packages
Change backup and auto-save directories to temp

Rather than clutter our working dirctories with auto-save and backup
files, keep them all in the system's temp directory.
Disable emacs' startup screen