Simul efun: age2dhm - converts an interger into a very short expression of time

Synopsis:
	string age2dhm(int a)

Description:
	Returns a string in the form "xd" for "x days" OR "yh" for "y hours"
	OR "zm" for "z minutes". 

Return value:
	returns an expression of time as a short string.

Examples:
	age2dhm(30) returns "1m"
	age2dhm(3600) returns "2h"
	age2dhm(43200) returns "1d"
	
Note:
	Age is measured in heart_beats and one heart_beat last 2 secondes!

See also: efun/time, efun/ctime