Add simple options for beginning and end of onion url

[misjoinder]

Adds feature requested in #3 to make it easier for someone to make a .onion URL without regular expressions.

Use -b to put at the beginning (./shallot -b namesame as ./shallot ^name) Use -d to put at the end (-e is already used) (./shallot -d namesame as ./shallot name$) Use -a to put anywhere (./shallot -a namesame as ./shallot name)