don't use chdir() to read config files

chdir() in Interrobang propagates the new working directory to programs
launched by Interrobang. Executing Interrobang in $dir should launch the
program in $dir, not in $XDG_CONFIG_HOME/interrobang, nor in $HOME.

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It is annoying if you use $XDG… — all your programs will start from Interrobang's config directory. Example:

    $ pwd
    /home/msthev
    $ interrobang # launching `pwd`
    /home/msthev/lib/interrobang

More practical examples: running e.g. `!term ranger` will start ranger in $XDG_CONFIG_HOME/interrobang, which is not really pleasant.

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I could have screwed something up with memory allocations (or anything else in fact), so please review the code before accepting it.