Add mkcd function to default bashrc.

[HT-7]

Seeing that there is some stuff in ~/.bashrc "out of the box", I think this needs to be part of the out-of-box experience as well:

mkcd() { 
	if [ -f "$1" ]; then echo "mkcd: Couldn't create "$1": file exists."; return 1; fi;
	if [ ! -d "$1" ]; then mkdir -p "$1" ;fi; cd "$1";
}

Sure, people who need something like mkcd can find it on the Internet, but those often less elaborate and lower quality versions than this one that lack the existing file and existing folder checks.

So I suggest providing every Linux Mint user with a uniform high quality version of this function.