Add a way to specify a command that runs directly before funk definition

[bbugyi200]

For example, assume the user inputs the following as the definition for a funk slc--meant to alias some_long_command:

# precmd: compdef {{funk}}=some_long_command
some_long_command

Then the resulting final funk definition should be

...
compdef slc=some_long_command
slc() {
    some_long_command "$@"
}

where ... represents the possibility of built-in (automatic) funk pre-commands---one of which would currently be unalias {{funk}} &> /dev/null.