Fix Issue #9: Make mbs-func <function name> find and open the function by default

Fix Issue #9: Make mbs-func <function name> find and open the function
by default

When navigating shell functions, it's nice to just be able to type
mbs-func <function name> and have it find and open the file. mbs-func
open works fine too, but this seems like it should be the default
behavior for now. If we start running into issues we can force everyone
to go back to running mbs-func open <function name> instead of just
mbs-func <function name>.