Fixes#18 by exiting the autoenv before invoking vim for editing the
`.enter` and `.exit` scripts, then enters the autoenv after vim exits.
This reduces the number of steps required to update the current autoenv
state.
usage: autoenv [-h] {init,edit,deinit}
options:
-h, --help show this help message and exit
commands:
init add .enter and .exit scripts in current directory
edit edit .enter and .exit scripts in current directory
deinit remove .enter and .exit scripts in current directory
Fixes#9.
