major refactoring
* aliases renamed to aliases.sh
* functions renamed to functions.sh
* ruby related functions extracted to functions_ruby.sh
* jumps extracted to functions_jumps.sh
* new function 'cmdtop' to show most often used shell commands
* some comments added
* g alias removed and git() function renamed to g() and simplified
* glcd() function renamed to gclcd()
mkcd() function moved up