Add `capture` and `stdout` commands (#495)

This adds two new commands as a base to enable users to use the output
of scripts to do certain actions in Joshuto.

The first command this adds is a third command to start a sub-process
beside `shell` and `spawn`, called `capture`. Like `shell`, `capture` is
running blocking but unlike `shell`, it does not release the terminal
but captures the `stdout` of the sub-process and stores it in an
`AppContext` attribute.

The second command added by this commit is `stdout`. This command takes
the output from the last `capture` run, stored in the `AppContext`
attribute, and uses it for some action. The action has to be specified
as a sub-command. As of now, only `stdout cd` is implemented. This
checks that the last output of `capture` is a single line of an existing
file or directory and then changes the working directory to that.

To get significant value from these new commands, `capture` needs to be
equipped with more variables to feed more information about Joshuto's
state into external scripts, and `stdout` needs to get some more
sub-commands.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/error/error_kind.rs b/src/error/error_kind.rs
index 1d68d29..915244b 100644
--- a/src/error/error_kind.rs
+++ b/src/error/error_kind.rs
@@ -21,11 +21,14 @@ pub enum AppErrorKind {
     Regex,
 
     InvalidParameters,
+    StateError,
 
     UnrecognizedArgument,
     UnrecognizedCommand,
 
     UnknownError,
+
+    InternalError,
 }
 
 impl From<io::ErrorKind> for AppErrorKind {