Smarter and more user-friendly shell command executions.

Provides wrappers around shell command functions from simple.el with
saner defaults and additional keyword arguments:
 - `friendly-shell-command-to-string' for `shell-command-to-string'
 - `friendly-shell-command' for `shell-command'
 - `friendly-shell-command-async' for `async-shell-command'

`friendly-shell-command' and `friendly-shell-command-async' can be used
as functions or commands (i.e. called interactively).

For detailed instructions, please look at each function documentation
or the README.md at
https://github.com/p3r7/friendly-shell/blob/master/README.md